JWF,
A google search using crayfish and pondboss should show a couple of links on crayfish. One I think was put in the archives section. Bill cody could probably find it quicker than I could and post it.

There was a link to a crayfish forum where there was good pictures and ID of many crayfish.

As to finding them, probably best off grabbing them yourself in a local stream. Rolling over stones and using a net is pretty easy way to do it. Or if it is a small stream you can sometimes use a minnow seine and cross the creek and then roll stones over and let things flow downstream to the seine.

When at a local lake you can throw in a minnow trap (metal type with cones on each end) and if there are crayfish in the area they will go in the trap providing you bait with something they like. I found catching some minnows or a small bluegill and then chopping them up to release the innards is a terrific attractant for the crayfish.

We leave a trap over night in the lakes we visit with a carcase of a bluegill after it was fileted, by morning there are dozens of crayfish and only the very clean bones of the bluegill left in the trap.

I have not found a commercial source for papershell crayfish or other desirable crayfish close by.

Native crayfish are best and non-burrowing are best.

Many lakes in northern michigan have big populations of very aggressive rusty crayfish. They are easiest to catch but the jury is out yet on whether you want them in your pond. If their numbers get out of hand you will have no vegetation which is important for supporting the food chain (small critters hide in vegetation and support the middle section of the food chain between microscopic and minnow size)

So probably catching your own native ones is the best.