You could make your own. Pick the same map everyone uses for ambush farms and customize the critters' powers so they only use pure negative attacks. The only problem with it is that your to-hit will be destroyed in seconds. So, it may not be possible to create a reliable high-speed farm for DA.
/DA actually has less negative resistance than it does psi. Cherrypicking psi enemies will end up with you having floored recharge, though - probably not a great idea either.
This thread on lowbie self pl farm maps has some good advice on how to set up your own and also some arcs that others have already posted up to be used.
http://boards.cityofheroes.com/showthread.php?t=263212
Global: @Kelig
I'm looking to level my new dark/dark brute. Anyone know of a good AE mish I could run to help level?
thanks in advance!