Apex monsters are the type to give that level of CP, but you often have to have a double EXP/CP campaign going, a decent chain, and a ring up. Without ring up, I think you can still hit it with a sufficient chain with the proper campaign and some bonuses, but yeah.

Apex mobs are best found in the gates zones, not the sub-zones but the actual zones. They're much stronger than normal ones of the same type, but their name (with the exception of things like Velkk) says Apex, so you know not to poke them if you're not ready. These do generally require a party, else you're spending ages killing solos.

What are you soloing to barely even get only 500 per kill? If you go to Reisenjima with even a 25% CP mantle, a few mission completions worth of CP bonuses, and the reive CP bonuses, you should be getting like 1100-1300/kill, if my memory serves. Toss on a Trizek ring or a Capacity ring and the amount goes up.