I guess it depends on what you consider a 'shooter'. I think that particular Genovese guy mentioned they had about 40 'good guys' or something to that effect. But I find it hard to believe that a 200+ soldiers and 1000+ associates family like the Genoveses only had 40 guys capable of violence.

Basically there's a difference between someone like Tommy Pitera or Harry Aleman and your average tough guy. Traditionally most crews(in New York or Chicago at least)have always had a lot of young tough kids willing to pick up a gun and shoot it out(there were a lot of those in the Colombo war in the 90s), but fewer pros.

So I guess the answer is a lot(during better times). But the majority of those would have more in common with Bloods and Crips than with 'professional hitmen'.