Most guys throw away their soft plastic baits after a day of fishing. Or they trash the ones they got but never use.

Does anyone know where I can get used, or unwanted plastic baits of any size, shape or color?

That first sentence is false. Replace "soft plastic" with live bait and then you will be correct.  Every guy I know keeps all of their baits after a day of fishing and if they dont like them they give them away after a few outings not one. 

I always have a dead pile of used baits in the bottom of my boat, usually throw them all away whenever I stop to gas the boat up. Not sure where you could get lots of used baits though. 

What are you attempting to do, melt baits?

jhoffman, yes I plan on melting baits. I have done this in the past and they work fine, and catch bass just like new ones.

I'd ask local fisherman/friends. They should be happy to give you used and broken soft plastics.

Post a wanted ad on this web site and other bass fishing web sites and see if that works.