Snub nosed SP101 marked .38spl DAO revolvers
Some time after the NYPD began authorizing RUGER revolvers as service revolvers, and off duty guns. The NYPD further spec'd that all revolvers purchased after a certain date be configured in DAO. All new smith&wesson, and all ruger revolvers HAD to be DAO. These revolvers may have been available in commercial gun stores, but for the most part they was purchased from the NYPD equipment section. (The NYPD has an FFL)
The move to autoloaders happen kind of sudden like. I'm sure this left a number of revolvers available to some jobber, though I have no idea what happened to them. Maybe the state department took them off their hands.
While the department transitioned to auto-pistols any revolvers still in service were grandfathered in to remain in service. Even though the department had stopped allowing new revolvers as service weapons, they continued to be allowed as off duty guns. Anyone who knows the NYPD knows how big it is, and how many actual gun's they have.
After the transition, one of the authorized pistol's is the Glock 19. As many have pointed out elsewhere the Glock 19 works as well in plain clothes, off duty and in uniform as a service pistol. Many officers (not gun guys) sold off their second guns. This put quite a few S&W model 36, 49, 10's 640's,and the rugers security six's in 2" round butt, and Ruger sp101's.