I have always stuck with a single supplier and verified with them that everything I want will work together.
That said, I use: http://www.model1sales.com/
But it's a Texas thing for me. I support local businesses whenever possible.
NRA Chief Range Safety Officer, Home Firearms Safety, Pistol and Rifle Instructor
"There are three classes of people: those who see, those who see when they are shown, those who do not see."
Leonardo da Vinci