I’m building off an idea I had in the Lower Your Axe suggestion by ArcenGaner.
As anyone who’s been to fangorn and used golden ent draught knows, huorns only come in 3 varieties:oak, beech, and birch. And in only one shape. My suggestion is straightforward: make it that huorns can be nearly any tree, and be any shape that that tree has. Not just the weird vanilla tree model, which isn’t that common on fangorn, so this will allow huorns to blend in better. Huorns (or dark huorns) should spawn in Eryn Vorn, which was part of the gargantuan forest that stretched in beleriland. The Silmarillion says ents lived in this giant forest, so logistically, there could be huorns in Eryn Vorn.