From what I can tell, the NYPD and RCMP were the last big departments using/authorizing the Smith & Wesson 3rd Gen 9mms. The RCMP is transitioning away and the NYPD dropped new authorizations of the 3rd Gens in 2014.
The new 5946s that have hit the market have night sights that are 2014-dated, suggesting that those pistols likely were undelivered or unissued NYPD guns. I've seen a post on another forum from a member who seems to be in-the-know at the NYPD that the Houlton-manufactured guns were problem prone and either caused or at least hastened the NYPD's dropping of the 5946.
S&W's position when it dropped commercial sales of the 3rd Gens was that they could make new production runs if a customer bought a big enough batch. With the last two big customers transitioning away, I think it's pretty safe to say that the 3rd Gens are pretty much dead as far as seeing new production.