...Including DGW, VTI and some other smaller outfits, it is fifty - fifty that the parts will work straight from the pack on older pistols. And this is even when the vendor tells me the part is a direct replacement.
The two I mentioned plus Numrich, and for ASP originated revolvers, Virginia Sutler in Winchester VA might be a good place to start.
Deer Creek in Waldron, Indiana has some parts for Non-Pietta/Uberti revolvers but the original parts are all but worked out of the system (I think).
So people who are selling you parts for an ASP or ASM (IMO) are actually just selling you parts that were made by someone else and they are the closest fit to the OEM.
Since you need several parts, I echo the previous recommendation to go to Cabela's and buy their parts kit for an 1858 Remington clone. If you find that the parts won't all fit, you can sell the stuff you don't need on eBay and you will get your money back plus.
It is on sale now for 29.99 plus forty dollars shipping.
I am kidding about the shipping. ;o)