Where's the best place to farm for red stones?

I haven't gotten any in months and just want to level my dragon

There are two kinds of Red stones. One is simply a red stone which is easily found by defeating the final stage on board 10 and is best saved for your inferno equipment. The other kind is a power stone and is only found in the dark dungeon at a very low drop rate. Since this one requires many to use on anything and is very hard to even get, it is best Used for nothing. Good luck.