Commercial tubing can be bought at a hardware store. PVC pipe is very strong and easy to clean and is available in a wide range of diameters from 5cm for mice. Corners can be made by buying elbow fittings. Ends can be bought to seal up the pipe. PVC piping is not flexible. Flexible tubing can be bought in the form of Ag-pipe from the hardware store. The disadvantage is that it must be usually bought in long lengths. It is usually black and has small holes along its length. Flexable tubing for mice can be made from vacuum cleaner hose.
Commercial tubing made from cardboard is also easy to find/buy. Postpak tubes from your local post office. The cardboard rolls from carpet can form tubing for your mice. You can ask your local floor covering store. The disadvantage with cardboard , is that it starts smelling from urine and the animals love to chew it. You will have to replace it regularly.
You may find that you have tubing from things such as toilet paper and ching wrap at home, these are suitable for your mice. You may consider taping some together, or cutting holes in the sides to form mazes.