NIS (now NCIS, of TV fame) did issue a RB 4" model 19, many of which were later transferred to the FBI. Regarding the model 66, there are published accounts of these being acquired (not through standard issue channels) for the SEALs, it being the only corrosion-resistant gun then available in a major caliber.
Model 15 's and model 39 9mm were available when I was on active duty,68 - ,72. I was in ordanance, UDT 21 and UDT 22, never saw a model 66 but heard they were around.
No one carries a 1911 anymore. They all disappeared circa 2004, along with the 686's and .22LR's.
The Mk23 is still around on a very limited basis, until the number of Hk45's arrive to replace them.
Sig 226 is the workhorse pistol. Most are Classic P226's, sans rails. The 226R was an interim replacement as the Classic 226's wore out. The Mk25 is so new very few have actually arrived, and without a holster...............they sit on the shelf doing nothing.