The part-time killers attempting to kill Maxwell Smart in the back of an ambulance.
Agency which supplies two phony ambulance drivers who attempt to kill Maxwell Smart who is acting as a decoy for wounded would be informer Russell Bediyoskin.
The men are apprehended but interrogating them proves useless because, not being regular KAOS personnel, they don't know anything.
[Mentioned, Episode #58: "A Man Called Smart, Part 2".]
Note: In Episode #55: "How to Succeed in the Spy Business Without Really Trying", Siegfried sates that he started out with KAOS as "an office boy and part-time killer" but contextually it seems unlikely that he was referring to a so-named agency.