https://www.thingsfromthebasement.com/-> I know you didn't want MDF... Buuuut these guys always looked good, and I got a few of their Sleepy Hollow buildings via their brief collaboration with 4Ground.
To balance out the unwanted MDF suggestions
- Grand Manner still do limited production of resin stuff in the UK
- Ironclad miniatures (Also UK) do a multi part fort, block house and a couple of small log buildings
- Perry/Rendera do some plastic cabins, barns and churches that should be available in the US (Albeit manufactured in the UK)
- Firelock games do a (I think resin) palisade fort as part of their Blood and Plunder range
Some of the OOP Architects of War resin buildings turn up on eBay occasionally. As a US company, I'd guess they are more likely to be found on US eBay than elsewhere