There are a lot of companies listed on the Scenery Source List that make kits, and can do built up if you like. The sources list is a post in the Scenery forum that includes links to many suppliers of o scale items for building your layout. This includes many smaller, unique and hard to find items.
Here is a link to the post.
https://ogrforum.ogaugerr.com/...c/scenery-sourcelist