Some hullmods require commission to buy. I am not sure about the emitters. Hardened Shields is definitely one of them, and the easiest way to get that hullmod if you cannot buy it is getting skill Defensive Systems 3.
Converted Hangar is an Open Market buy, if available. Since no ship uses Converted Hangar in unmodded game, it is not found for sale, and the easiest way to get it is Fighter Doctrine 2. In modded games that include ships with Converted Hangar, that hullmod is fairly common in Open Market.
Hullmods used by the enemy can be dropped as loot, but that happens rarely. But it will happen eventually if you farm enemies and fight much.
If you have Salvaging 3, looting research stations (while you have three or four rigs in your fleet), can yield some nice rare loot.
As for what MajorTheRed said, without commission, grinding enemies until one drops is probably the way to get ITU.
P.S. If you want to buy most of the really nice hullmods that require commission to buy, join either Tri-Tachyon or Persean League.