This is too generalized. When I recruited for finance/pharmacy easily get 10+/mn, at top tech company averaging 1-2/mn. It really depends on roles, for head hunters doing executive level positions they probably only fill a few a year because the search for one takes a long time.

3-5 a month is pretty optimistic. I wouldn't want people to think this and leave their jobs. If you do two a month you're probably doing quite well, especially if you're independent, but it's not easy as an independent to do volume.