I found the same problem with the "rail" they put on this gun, which is why I didn't purchase it. There are also no holsters for this gun with a light I found, so it really is kind of a waste, which sucks because I loved the feel and balance of the gun. That said the re is the TLR-3 which I know fits, but it wasn't out yet when I was looking. There is also the Insight X2 (which is junk) which will also fit. Neither are very bright (probably due to the batteries which can fit), and like I said, good luck finding a holster (if you need one, I did).
Good luck, it just seems there isn't a large market for the subcompact lights.