Idler wheels sound like something that you could make. Some years back I picked up a very old 1 x 42 belt sander. It's the one that I see on one of the antique tools website. The bottom, 4" diameter, die cast, idler was badly deteriorated. I was able to get a piece of 1" thick aluminum. I drilled a hole and bored it for a 1/2" ID bronze bearing. I pressed the bearing in place and using the bearing as a center, mounted it in a metal lathe and turned it down. It's been working good for over 3o years now. I would expect that you could do the same thing with Baltic Birch plywood and could probably rig up something to do the turning on a wood lathe.