There is no "source" for original percussion era Colt parts. The only way to get antique parts is to take them from an old gun. Thus, the source is the Internet and a lot of hard research and calling around. EBay is a good place to try. You can also try
www.coltparts.comThere are several vendors of antique parts like Poppets, Jack First, Wisner's, etc., but them having a particular original part for a Colt percussion revolver will be simply a matter of luck that they have it when you are looking for it.