Right... just had a brief mosey around for shirt & tie clad cops with a 'sam brown' style pistol belt which the 50's pics seem to show:
Brigade Mob Wars - Probably too 30's (tunic, no pistol belt); but I imagine the state-troopers would work well enough for STs
Pulp - Great coats, and looking very 20's
Coppestone Gansters - Better, tunic but with the right sort of
Warghames foundry Street Violence: Shirts & Ties. No cross belt forthe pistol (but there is always gren stuff) and there are a large number of women cops in the pack. I don't when women coppers becmae comon in the states, but i'm guessing it certainly wasn't the 50's.
Dixon Gangsters - Tunics, no pistol belts
Geezers - Were talking about doing 70's US cops, but no sign of them thus far...
If money was no object, then I guess the Foundry figures with a bit of conversion work (crossbelts, removing any too modern looking belt kit - e.g. hand held raido's) and selling on the women would do it...