I mean, what themes? Theres terrain out there to fit every realm. Just paint to fit. What are you looking for, I’m sure I can point you to something.
I’m not personally a huge aos guy, I play CoS, but I’ve played twice in the last year. All of our gaming here is Fantasy/Old World (9 games in, and a tournament coming up two weekends from now) and the odd historical game and has been for decades, so I don’t care about that, but aside from endless spells, GW doesn’t make any special terrain. If GW makes it, you can get a nicer version printed elsewhere. GW terrain mostly isn’t nearly as good as other places. GW’s chinese made terrain is their worst product imo.
and almost every town/city has a 3d printing service if you want printed terrain and don’t have an fdm printer of your own. Frankly, a printer was the best decision I made for terrain, it saved me thousands. My game room has 4 tables, and I have at least a dozen terrain setups. Currently painting a Sphinx and statues for my desert table.