As far as I know, only the Centennial models are currently available without the lock. And although I have no way of knowing for certain, I suspect there is a reason for that. It's a "cover your butts" measure by S&W. Allow me to explain. The J-Frames are marketed primarily as self-defense weapons, the DAO models even more so (SA/DA, adjustable sighted, longer barreled kit guns and target models being obvious exceptions). In the extremely rare, but high-consequence event that a lock fails at a critical moment, S&W can say that they offer revolvers specifically for self-defense that do not have a lock, and the complainant should have been using one of those models in that capacity.
Secondly, the IL can be engaged with the cylinder fully loaded. Other than the hammer flag, there is no expedient (read lazy) way to positively check the status of the lock. No exposed hammer means no hammer flag. "Gee, is this here loaded gun locked or unlocked? Well, I reckon I'll just try to pull this ol' trigger to find out..."
Absent any way to confirm this observation, I feel just a bit too cynical offering it, but this makes sense when trying to explain why only the Centennial models are offered without the lock. Sorry, but I'm not buying the line that S&W found some old Centennial frames tucked away somewhere, and they are slowly using them up.