I just bought a 642 and have ordered Mika round and square-cut pocket holsters. However, I also want a Kydex IWB. All the usual makers make them for the 642 (Blade-Tec, Comp-Tac, FIST, etc, etc), although I don't think that most have retention straps standard.
I think I've decided on the Comp-Tac Two O'Clock that D-Man mentioned - it's tuckable (although I probably wouldn't tuck it, it's nice to have the option), and it's actually designed to be carried appendix-style instead of the usual behind-the-hip position, which is where I think a snubby belongs.
FullEffect1911 asked why synthetic? I prefer leather for field holsters because they look nicer, but I think Kydex is more practical because it's waterproof and it can be made thinner than leather. Kydex is ugly, but if it's IWB, you can't see it, and IWB holsters need to be as thin as possible. Plus, there's not much point on putting an ugly gun like the 642 in a nice-looking holster.