Yeah, mossy is going to be tough right now for 1.1.2 worlds. I believe the plan is for Obsidian towers to be somewhat rare when 1.2 goes out, but right now all of the towers are obsidian. That being said, I'm not sure the other towers will be mossy / stone though... so this may just be a thing now. I don't know of any other easy way to get moss balls for repair.
I added my own temporary recipe for it since I enjoy having it available for repairs earlier on, it's a water bucket or clay water bucket surrounded by cobblestone. If anyone wants it:
#Mossy stone
recipes.addShaped(<98:1> * 8, [[<4>,<4>,<4>],[<4>,<326>,<4>],[<4>,<4>,<4>]]);
recipes.addShaped(<98:1> * 8, [[<4>,<4>,<4>],[<4>,<25968>,<4>],[<4>,<4>,<4>]]);
Also, I found a few flint and steel in the roguelike chests, I'm not sure we're supposed to be able to get those easily, but if not it should probably be removed from the possible loot.