I've gotten my DWE's using a light ship (iEagle) with a wake scanner. Find a high traffic port, preferably in solo as CMDR presence always messes up NPC behaviour, and just scan the wakes as fast as you can. My preferred spot is Jameson Memorial in Boom. If you don't have access to that port, use eddb.io to find your nearest high population high-tech port that's currently in Boom.
Chemical Manipulators I just do the scavenger way. Jump into a Combat Aftermath or Encoded Emission. Stick to the Shiping Lane zones in the system. They're usually between the arrival star and the populated planets.
You get plenty of both doing this. I did around 2-300 FSD rolls in a few weeks that way. Doing other suff in between.