photopolymer plates?

www.boxcarpress.com
I get my plates made by them, they also sell unexposed plates and platemakers

Boxcar is a great source, and they are letterpress experts so the support for your questions would be great there. I have also got plates from a company called Anderson Vreeland, but they supply to alot of the print industry and may not be as letterpress-centric as Boxcar.
As for processing them at home, you have your work cut out for you. I make plates almost daily in our pressroom using a platemaker bought through Boxcar. It was an expensive machine, but it would be difficult to reproduce the process without it.
The plate requires being exposed by concentrated light, while vacuum sealed to your film negative. Then washed out against soft brushes in a temperature controlled water bath, then dried under warm air, then exposed again under the concetrated light for final hardening.
One might be able to rig/build a system at home, and the washing can be done by hand, but alot of trial and error would go into this.
I would try to take a platemaking class or spend some time making plates on someone else’s processor on order to learn all the steps in detail. The San Francisco Center for the Book offers classes in platemaking.
Maybe there is a local resource in your area that could offer instruction.
-Good Luck out there!