Complete the quest that brings the law back to Primm, then go do about 2–3 quests that go in the Vance Casino and walk around. Deserters should talk to you.

Kill them or scare them away. Do 2–3 quests again, than come back.

It's a real casino now! Use all your caps, NCR money, and legion money.

Then keep cashing your chips for caps. The real trick is they take gamora chips not their chips.