I've found very few adepts. I think I have 4 skills total at adept, the rest are app 3 and 4.
I have found 2 myself, another two I traded and bought.
Keep in mind, adepts are supposed to be the mid-range of rare, master are the rarest. Also take into account that there are tons of abilities in all, you probably wont see any of the higher adepts drop frequently till you get into the access zones.
I'm just guessing but are you mostly killing in Commonlands, Nek, and TS with the occasionaly sub-zone? Have you done the Zek/EL access quests and started hunting there?
There is still a lot of uncovered ground to explore.