Unfortuantly, I think Ebay may be the best, or least the most common, source for disco'd stuff. It would be intersting to know what manufacturers do with all their disco'd wheels. They are aluminun so they could just melt them down, but I dont' think they would do that wholesale to complete lines and inventory.
If you do find a decent source, I'd love to know. There is a wheel I have that I'd like to find another pair of.