HGEs for Proto Radiolic Alloys / Proto Heat Radiators are relatively easy to find - just hop about and look around. Pharma Isolators you might find occasionally.
Missions for Exquisite Focus Crystals and Biotech Conductors are also very common once you're allied with enough factions.
The rest you can get in small quantities by shooting at high-end NPC Anacondas, or by material trading. Or just stick to the G4 blueprints, of course, which are still pretty good.