The fastest way to find these items is to check out the personal shops (category: Miscellaneous - Remodeling Goods). Although I'm not saying the price is reasonable
Currently in NA server, it looks like FUN scratch is the main source of non-standard items other than basic theme and city area. The ongoing FUN scratch has Scenery Pass: Volcanic Caves and Gothic Theme. Scenery Pass: Forest & Classic Theme was available in the past.
And just to make it sure, the scenery passes and room themes are different things. Scenery changes the outside of the personal quarter, room theme changes the inside.
Maybe they'll add some extra choices on Furnishing Shop, FUNporium, or Badge Exchange Shop in the future.