This list and topic should be heavily edited to retain Sticky status
Even with the original post, it has less to do with sourcing than listing of certain chemistries available at that time. Few links. And it reviewed chemistries with opinions that had little basis in experiential fact. Sorry, Greg.
A lot has happened in C-41 chemical availabilities since the original post. (I can't speak to RA-4, as I don't do that process. But I imagine something similar.) B&H won't ship liquid chemistries, nor do they stock much. But for someone in Manhattan willing to wait, it's still a source. Freestyle has attained the Rollei/Compard and Tetenal liquid chemistries.
http://www.artcraftchemicals.com now has all the individual chemicals you need to make C-41 from scratch, if that's your gig. I did some calculating, and for about $108 plus shipping you can get everything you need to make 45 liters. The chemical that runs out at that point is the half pound of CD-4. There are various amounts of all the other chemicals left at that point. Also chemicals to make your own bleach and fixer, if you wish.
Mi dos centavos.......