I haven't noticed a correlation between which pets drop which type-specific stones. Then again, I've only gotten about 5 or 6 stones from wild pet battles so far (a generic, beast, critter, humanoid, mechanical and aquatic, I think). It usually just happens when I'm leveling pets random places - so ...

Dragged the guildies along to run AQ with me last night before the raids reset. I think all 5 of us managed to get almost all the mount drops (except the elusive red one). And I got a mini mindslayer and anubisath idol. The only one that didn't drop was the viscidius globule. But given that raids re...

On Moon Guard the going rate is about 5k, then again - I don't know if any are actually selling for that but it seems a little more reasonable.

ETA: I would absolutely sell un-soulbound ones, I get plenty of type-specific ones from dailies.