I was looking for some a couple of days ago. Three hours of looking and I only found two High Grade Emissions (three CDC's in all). High Grade Emissions are probably the most annoying thing about engineering right now. There have been people reporting difficulty finding them after the release of 2.4, which seems to be an acknowledged bug. w3bbo says get them by bounty hunting, although I've never found them that way when looking. Worth a try though.
If you must look for HGE's, then I'd suggest a high pop Fed system in 'None' state.