You lvl explain the lack of it it should start showing up soon though, and gunners are normaly great for getting it provided you are high enough lvl.
Just lvl up a bit and it will become easy to find(ofcourse than youll want sturdy version of it and once you have that the heavy one since lether,metal,combat and synth armor actualy come in 3 tiers-normal, sturdy and heavy)
Yeah as others mentioned just using the words combat armor isnt enough. There are three tiers of it, all visually distinctive. I get the feeling you are not talking about the lowest tier, which shows up around level 20. The next tier, starts showing up at 30s, and after that.. 40+.
All an all its an annoying system that needs to be modded. Even if its something as simple as adding in a negative prefix, so you get the same stats as lower tier armor, but the looks of a higher tier. (Like Used heavy armor)
I am about level 35 at the moment, and I have combat armor coming out my ears.......
I'm virtually swimming in all kinds of combat armor. Enemies drop them by the numbers. But it's on the middle ranks, not the grunts, you encounter early in the game.
I found a Gunner Boss in Hub City Auto Wreckers always has Heavy Legs, Chest, and often an Arm. She has a Fatman and is often too accurate when trying to Snipe.
Normal Combat Armor just requires a long walk to Jamaica Plain and loot the set Sal is wearing, and bring lots of cheap ammo for the Residents
There's actually a lot to be found early in the game, if you explore and if you survive. I haven't bought a single piece of armor from any vendor. I improve what I find. It's usually better than what's for sale.
Also keep in mind, that most places that are NOT settlements, respawn pretty quickly.... So, even if you take out the gunners at level 4, but the time you hit 20, they will most certainly be back. There are a selection of places that I hit fairly regularly to farm raw materials.
Only real upside to getting a high level before exploring are the static power armor spawns. Explore certain areas at a low level, chances are good you will get the lowest level power armor. Explore that same area 30+ and there is a good chance you will find a much better and rarer set. Other then that, stuff respawns fast in this game.