These achievements were annoying on 2 fronts: 1) Finding the solo champion level NPCs, and 2) grinding. After finding the NPCs, I swapped back and forth between Pub and Imp toons to avoid needing to wait for spawn. Also used my Rampage Achievement boosts which lasted most of the time (9 boosts got me to 90/100 for both sides).
Makeb: Ransacking the Republic (Imperial Side)
Solo champion guard:
-2136,2388
Map Area: Volcanic Mesa
Northeast Corner
Approach: from the north going east (avoid coming from the south as you'd have to go through Pub shuttle area). He is hiding behind a stone. Recommend pulling him out from behind the stone by hiding in outcropping at -2173,2403. Watch out for knockback, this is near the edge of the mesa.
Makeb: Pillaging the Empire (Republic Side)
Solo champion guard:
-3168,2397
Map Area: Solida Hesk's Estate
Southwest Corner
Approach: Can QT and then head directly south and jump the gap to the Imp side. There is a lone "Imperial Special Unit" sitting right at the front before going into Imp shuttle area. Can pull him up the hill a smidge to remove risk of aggro other units.