McMaster/Carr catalog - plastics
Here are some plastics and there uses. This site is a little industrial but they have almost everything. Acetal/delrin is often used for suspensions. As well as nylon and teflon.
Locally, you might be able to find a plastics supplier that sells rem's. That way you can buy something now and you may not have to buy 5ft or whatever minimum.
Those are some good tips on checking your leaf springs, D-man. I'll try cleaning or at least greasing my leafs and see what happens.