If you want to carry it with the light rail attached, you're going to have a problem finding one.
I have a Milt Sparks Summer Special 2 for my TRD 325. It's IWB, which isn't what you're after, but I had the same difficulty in finding a holster. Tony Kanady and crew were great to work with but I ended up sending them my gun because they couldn't get a dummy from S&W and didn't have enough orders of that model to justify buying a real one. The shipping costs were about the same as the holster price. It was worth it; the holster is fantastic and holds the gun tightly against my side. They now have a disclaimer about S&W Performance Center guns on their website.
If you don't want to carry it with the light rail in place, most N-Frame holsters will do, but that defeats the purpose. I have my light rail loctited in. The idea is to be able to slip the light on when needed (for me, in the nightstand) and carry it without the light but with the rail all day long.
Good luck.