Are there every going to be any scenery passes aside from "basic" and "city", since they seem to be the same anyways? If there are already other ones in the game, how do you find them? Drops, scratch tickets, random combinations of 37 different currency exchanges while the moon is full? 
Usually from scratch tickets. I had the Japanese / cherry blossom scenery (purple-pink sky/sunset-like) drop from a FUN Scratch in JP once.
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.
Is there a way to switch to a previous scenery I've used before or is really just one time use and is not permanent like music :(?
@Merelambasted You can save up to 3 settings but one is needed for every room as it registers to that room. You can switch between the section a and b and small rooms however.
@Merelambasted Scenery Passes are one time use, so in order to use a previous Scenery, you need a new Pass for it, same with Room Themes.