OH and BTW 38 Super is used by the US Secret Service Counter Assault Team (CAT)
For everyone saying they'd use 10mm - it's used by the FBI Hpstage rescue team, in their MP5/10A3 submachine guns.
I'm not sure about this one - but I thought National Park Service rangers were issued a 44 magnum carbine at one time maybe the Ruger Deerslayer? Maybe those aren't around anymore, but it only takes a grandfather clause and a couple of old agents still using it to make it off limits to the public I would think.
When you start to look at all the myriad calibers that Government uses - you're left with stuff like 41 cal, 9mm IMI, 9x25 Dillon and similar...