There are a couple of scenes in The Avengers in which Loki has human soldiers working for him-- the battle in Germany, and the fight on the Heli-Carrier. When asked by one of his turned allies (Hawkeye, I think), where they came from, Loki handwaved it by saying that SHIELD has enemies.
A handwave is a throw away line used to explain an important plot detail. The hand wave being we have no idea what the motivation or identity of these faceless goons are besides being evil cannon fodder.
No plot detail could have been more unimportant. It’s like asking who was Ernst Stavro Blofeld’s hiring manager and what benefits did he offer should the cannon fodder actually survive.
Yeah, worrying about how the guy who can mind control Avengers is finding goons seems pretty silly. This is one of those things that don’t even need an explanation.