I'd say requesting non-casters in a dungeon is pretty much impossible to find, this is due in great part to the XP bonus you get for dungeons. The caster's are what make dungeons so difficult IMO.
Some places I can think of that the caster's aren't as bad would maybe be:
- Paw
- Highpass Keep
- Kaesora - Spiders and Skelles dont cast really, Spider's however do Poison.
- Permafrost (you may be too high for here)
These are all underpopulated dungeons which makes it easier even with casters because you can just clear the path and keep pulling to zone. You run into trouble GTFO. I'd say that Paw would be the best place for this strat.
Also, you could try investing in some resist gear. That could help quite a bit.