Just wondering - where did they find all these extra guys, "button men"? For instance, in prt I - after the whole hospital, Michael getting punched scene - they get home and the house is surrounded, Clemenza says looks like a fortress - where did they find all these guys? And how did they not know these guys were working for one of the other families?

Both Tessio and Clemenza had substantial regimes of made men and associates who ran the rackets that generated the cash for the Corleone family. In time of war, those men could be taken out of their regular livings to pull guard duty at the Corleone compound and to "go to the mattresses," as we saw later. There were plenty of 'em. You heard Sonny order Tessio to send "50 good men" to guard the compound. Later he told Michael that "a hundred button men" were on the street looking for Sollozzo.

The book discusses the fact that Vito isolated Clemenza from Tessio. One could reasonably assume that Vito isolated Clemenza from a lot of his business dealings and relationships. Therefore it is reasonable to assume that the Corleone's had "firepower" that Clemenza was not aware of.

Then again, Sonny or Tom may have just looked up "wiseguys" in the yellow pages.

In reading The Sicilian in which Michael and Clemenza make an appearance, it is mentioned that Clemenza regularly makes trips to Sicily and recruits a number of men to come over to America to be part of the Corleone/Clemenza regime.

How'd they find em? I would bet they were like Henry Hill and them. Just hung around the "men of respect" in the neighborhood ever since they were kids and just stayed around them.

In Vito Corleone's day, the Mafia was a kind of "employer of last resort" in some Southern Italian neighborhoods--like the phone company was for WASPs. Kids who showed initiative but were unwilling or unable to get jobs or education in the legit world were watched by the local Mob capo. Those who showed promise were brought along, tested, eventually inducted.