Here is a list of every Oz book I could find. Any that are on the internet I have linked so you can read them online. A lot of these are very obscure and the chances of finding them are rare...These books are listed in chronological order of how they happened in Oz, not when they were published. 
1. Lurline and the White Ravens of Oz2. The Roots and Wonders in Oz
3. How the Wizard came to Oz
4. Moonstruck in Oz
5. A sure cure in Oz
7. The Tin castle of Oz
8. Dorothys Mystical Adventures in Oz
9. The Magic Chest of Oz
10. Father Goose in Oz
11. The Speckled Rose of Oz
12. Denslows Scarecrow and Tinman
13. The Marvelous Land of Oz
14. The Third Book of Oz
15. Ozma of Oz
16. The Nome Kings Shadow in Oz
17. The Song of Oz
18. Dorothy and the Wizard in Oz
19. Oz and Three Witches
20. Dorothy and the Magic Belt
21. Dorothy and the Seven-Leaf Clover
22. Mr. Tinker in Oz
23. Ozma and the Wayward Wand
24. Dorothy and Old King Crow
25. Dorothy of Oz
26. The Rewolf of Oz
27. The Road to Oz
28. The Crocheted Cat in Oz
30. Starglory of Oz
31. A short Story of Oz
32. The Cowardly Lion and the Hungry Tiger of Oz
33. Little Dorothy and Toto in Oz
34. Tik-Tok and the Nome King of Oz
35. Ozma and the Little Wizard of Oz
36. Jack Pumpkinhead and the Sawhorse of Oz
37. The Scarecrow and Tin Woodman of Oz
39. The Littlest Giant of Oz
40. Tik-Tok of Oz
41. The Patchwork Bride of Oz
42 The Scarecrow of Oz
43. Masquerade in Oz
44. Rinkitink of Oz
45. The Lost Princess of Oz
46. The Tin Woodman of Oz
47. Wooglet in Oz
48. The Magic of Oz
49. Glinda of Oz
50. The Ork in Oz
51. The Emerald Ring of Oz
52. Invisible Inzi in Oz
53. The Royal Book of Oz
54. Pegasus in Oz
55. Ridiculous Rivals in Oz
56. Kabumpo in Oz
57. The Joust of Oz
58. The Cowardly Lion of Oz
59. Grampa in Oz
60. The Haunted Castle of Oz
61. The Lost King of Oz
62. The Gnome King of Oz
63. The Silly Ozbuls of Oz
64. The Silly Ozbul of Oz and Toto
65. The Silly Ozbuls of Oz and the Magic Merry-Go-Round
66. The Giant Horse of Oz
67. Jack Pumpkinhead of Oz
68. The Forgotten Land of Oz
69. The Yellow Knight of Oz
70. Pirates in Oz
71. The Purple Prince of Oz
72. Rosine and the Laughing Dragon of Oz
73. Two Terrific Tales of Oz
74. Ojo in Oz
75. Jimmy Bulber in Oz
76. Speedy in Oz
77. The Wishing Horse of Oz
78. Captain Salt of Oz
79. Handy Mandy in Oz
80. The Silver Princess in Oz
81. Ozoplanning with the Wizard of Oz
82. The Mystic Planes of Oz
83. The Wonder City of Oz
84. The Tired Tailor of Oz
85. The Green Goblins of Oz
86. The Dinamonster of Oz
87. The Scalawagons of Oz
89. Luck Bucky in Oz
90. A Runaway in Oz
91. Umbrella Island of Oz
92. The Magic Cryptogram of Oz
93. The Magical Mimics in Oz
94. The Giant Frogman of Oz
95. Queen Ann of Oz
96. The Shaggy Man of Oz
97. The Red Jinn of Oz
98. The Hidden Valley of Oz
99. The Wicked Witch of Oz
100. Jubilee in Oz
101. Traleewu in Oz
102. Yankee in Oz
103. Merry Go Round in Oz
104. Christmas in Oz (Toto and the Cats of Oz, vol. 1)
105. The Blue Emperor of Oz
106. The Raggedys in Oz
107. Mr. Flint in Oz
108. The Gardeners Boy of Oz
109. The Braided Man of Oz
110. Egors Funhouse Goes to Oz
111. The Flying Bus of Oz
112. Dorothy and the Wooden Soldiers
113. The Enchanted Island of Oz
114. Button Bright of Oz
115. The Forbidden Fountain of Oz
116. The Disenchanted Princess of Oz
117. The Sawhorse of Oz
118. The Enchanted Appled of Oz
119. The Secret Island of Oz
120. The Deadly Desert of Oz
121. The Ozmapolitan of Oz
122. Toto in Oz
123. A Viking in Oz
124. Kidnapped in Oz
125. Veggy Man of Oz
126. The Colorful Kitten of Oz
127. The Silver Shoes of Oz
128. The Marvelous Monkeys of Oz
129. The Ice King of Oz
130. The Enchanted Gnome of Oz
131. Summer Solstice in Oz
132. Acinad Goes to the Emerald City of Oz
133. Maybe the Miffin
134. Hurray for Oz!
135. Barney Backhoe in Oz
136. The Forgotten Forest of Oz
137. The Magic Diamond of Oz
138. Dagmar in Oz
139. The Giant King of Oz
140. Skeezik and the Mys-tree of Oz
141. The Rubber Ostriches of Oz
142. The Bunny King of Oz
143. The Three Imps of Oz
144. Our Trip to Oz
145. Lunarr and Maureen in Oz
146. A Wonderful Journey in Oz
147. The Enchanted Emeralds from Oz
148. Time Travelling in Oz
149. The Mysterious Caverns of Oz
150. The Magic bowls of Oz
151. Beach Blanket Babyloz
152. The Knock-Kneed Knight of Oz
153. The Lunchien Forest of Oz
154. The Magic Tapestry of Oz
155. Do it for Oz!
156. The Yellow Hen of Oz
157. The Enchanted Patchwork Quilt of Oz
158. Bungle and the Magic Lantern of Oz
159. Many Lands of Oz
160. A Million Miles from Here is Oz
161. Kaliko in Oz
162. The Enchanted Cat from Oz
163. Dunderheads in Oz
164. Three-Heahed Elvis Clone Found in Flying Saucer over Oz
165. Sinsister Gases from Oz
166. The Fantastic Funhouse of Oz
167. Gambu in Oz
168. Ruggedo in Oz
169. The Magic Talisman of Oz
170. The Liberty Bell of Oz
171. The Fairy Circle of Oz
172. The Odd Tale of Osoenft in Oz
173. The Amazing Ozosphere of Oz
174. Red Reera the Yookoohoo and the Enchanted Easter eggs of Oz
175. The Blue Witch of Oz
176. A Queer Quest for Oz
177. The Case of the Framed Fairy of Oz
178. As the Clock Strikes Oz
179. Sky Island of Oz
180. The Magic Ruby of Oz
181. Ozma gets really pissed off and cusses and totally offends (almost)
everyone in Oz.182. W.W. Denslow in Oz
183. Sail Away to Oz
184. Fwiirp in Oz
185. The Giant Garden of Oz
186. Cory in Oz
187. Brewster Bunny in Oz
188. The Healing Power of Oz
189. The Haunted Hot-Tub of Oz
190. John R. Neill Visits Oz
191. The Wogglebug of Oz
192. The Reading Tree from Oz
193. The Magic Dishpan from Oz
194. A Valuble Gift from Oz
195. Brwester Bunny and the Case if the Outrageous Enchantments of Oz
196. A Silver Elf in Oz
197. The Shifting Sands of Oz
198. I want to grow up in Oz
199. The Lost Emeralds of Oz
200. A Murder in Oz
201. Dr. Angelina Bean in Oz
202. Bicketheads of Oz
203. Bik Wish in Oz
204. Polychrome of Oz
205. A Small Adventure in Oz
206. A Time for Oz
207. Trubbles in Oz
208. The Wise Ol' Owl in Oz