Haven't read the series, but I know the US Secret Service and the US Air Marshal Service both issued .357Sig P229s. Secret Service recently began switching to Glock 9mm (or are about to). I don't know if the Air Marshals are still being issued .357Sig P229s.
There may be other federal agencies I'm not aware of.
Also, some federal agencies allow, or at one time allowed, personally-owned weapons, but I think they were limited to standard issue calibers, so I don't know if .357Sig was included.
I know there have been state agencies that issued .357Sigs, but other than Texas DPS (which switched to 9mm maybe a few years ago) I can't remember them offhand. Texas Rangers were, and maybe still are, allowed to carry a pretty wide variety of personally-owned weapons.
And there are state and local agencies that allow personally-owned weapons, sometimes with a wider latitutde given to weapon and caliber choices than the feds.
