I'm a dozen or so hours into the second region and I still haven't found a single piece of heavy armor, and I was hoping to specialize in it. Where should I go to get some early on?
You can't effectively specialize in Heavy armor until midgame. If you really want to, just hold onto all the heavy prices you get. The "set" bonus from the Bear school perk won't be worth the armor difference on the lower level gear, but that's the only way to get it done.
Heavy armor doesn't seem to show up with any regularity until around level 20. There are heavy gauntlets in the tomb right next to the PoP guarded by a wraith in the starting area, but that's the only guaranteed heavy armor I can think of early on.
Mechanically, you'd want to wait on the armor specialization until you can craft Witcher gear, when the trade off of holding onto slightly under-leveled gear is worth the bonuses Witcher gear provides.
Sorry this isn't the answer your looking for, I felt the same way on my second (Ursine set) play through.
For some guaranteed Heavy Armor, you could try the Ursine Armour scavenger quest.
This starts on Skellige, and is suited (apparently) to folk around level 20. The armor is then upgradable, for use further into the game.