Actually it is slide stop S&W does not recommend to use it as release...
EDIT: sorry, back to original question - I haven't seen any aftermarket slide catches for sale; the best bet probably would be midway, they have lots of parts for all kind of makes and models.
It was a matter of time before someone posted that hahaha.....i use it for ameture competition so useing it as a release is a must...but i know i had that "arguement" with the guy at the gun shop to but its all good i know where your coming from