Crunch, Dark Pulse... *Goes on the internet* Night Daze, Foul Play, and Sucker Punch. And don't forget every generation there are always new Moves, so you can expect some new dark type moves. (It doesn't mean that they will be very strong or not.)
A dark gym could easily fit in the 6th/7th gym category.
A dark gym could easily fit in the 6th/7th gym category.