If I was a bit more proficient in Linocut (cutting blocks of linoleum, like i did with the Ducal Guard stamps), I would offer to make them out of it. However, since the Linoeleum has a bit of give to it (kinda shift and squishes around when you work with it), it would be hard to make any sort of detail. Best to use a straight up hard surface and then etch the crap out of them. For do-it-yourselfers, I would recommend clay or ceramics. Get a nice hard kind that wont chip easily after baking: wouldnt want your stamp to break after an accidental mis-handling.
There are macquette making materials out there that is *like* clay. Its not really good for durability, though. The upside is that you can get a good amount for cheap, and its made to be baked in a home oven.
Carving rubbber would be a good idea, too. Just make sure its a nice stiff rubber, or it'll end up just like the linoleum. I would also offer up the possibility of wood burning as well. All you would need is small wood chips and a soldering iron. Careful with the iron, though, those things sting. The good thing about wood burning is that anyone with *some* sort of inclination of art skills could do it.