It is quite easy to make light and robust wheels from Depron foam, 3mm or 6 mm thick, depending on the size of your model. Punch tools of various sizes can be made using plumbing coupling devices of various diameters.
I am pretty sure your next question will be : How do I find the center of these bloody discs I have just cut ? No panic. Just cut a piece of cardboard (wall calendar for instance) with an 45 ° angle and tape it as shown below on a mechanical square. Isn't that easy ?