Scott,
I think Hobby Lobby would be your best bet for small scale casting..(just a few parts at a time.)
https://www.hobbylobby.com/Crafts-Hobbies/Clay-Molding-Sculpting/Casting/Amazing-Casting-Resin-Kit/p/22272
https://www.hobbylobby.com/Crafts-Hobbies/Clay-Molding-Sculpting/Casting/Mold-Putty/p/22271
https://www.hobbylobby.com/Crafts-Hobbies/Clay-Molding-Sculpting/Casting/Mold-Putty/p/27710