You can still find DWE's by scanning outside busy stations
I stopped going to distribution centers long ago as i found it a bit boring, I stuck a wake scanner on my main trading ship and used it once everytime I left a station... I've never run short yet
Another thing you can do is trade. A little more work maybe, but federation systems have been spawning CDC and other G5 stuff pretty well. You could stock up on those and trade out for chemical manipulators you need.