The approach goes smoothly, there appears to be no danger.

The meeting place is camouflaged from a distance, but you can only hide an entire camp of people so well.
The man named Blackwire (matching the description given to the exiles) sits at the center of the camp, eating his dinner as his underlings tend to the chores around him. Sean counts two whole gangs' worth of raiders at the camp. 22 people with guns, two cars and 10 motorcycles. Approximately, half of them are injured, and five of those injured are too wounded to do anything but rest.

The bootstrapped shotgunners and Sean keep watch from afar as Richard approaches to talk to Blackwire. Despite the camp's paranoia, Richard is allowed to come over and discuss the situation.

Sean proposes our position in the negotiations would be as follows:
1. Too many of those who want Blackwire dead would rather kill him than negotiate a truce. We are unable talk them off that at the moment, but...
2. We have been told by the rangers that one Blackwire is worth two other slavers' commanders. So, if we can get two slavers' commanders with the help of Blackwire, things are bound to improve substantially.
3. Then we would be able to house Blackwire somewhere, employ him in our operations and reasonably demand he is not attacked by forces allied to us and opposed to the slavers.
4. So our proposal would be that Blackwire either gets two such commanders himself or hands us the information about all such commanders so that we can choose and get two of them.
5. If he chooses the later, he'll have two options until we are done: either to continue to be on the run or to to surrender and be held prisoner (we can reasonably demand him not attacked while we hold him prisoner).
6. Alternative proposals could be considered, but no guarantees.
7. If Blackwire needs food stock to lie low, or whatever other supplies, we can trade with him, for either material things or the info.
Blackwire enjoys a bowl of hot soup as Richard outlines what's going on his end.
He admits that he may have to stay in hiding for a good long time, with the exiles' help.
Blackwire tentatively suggests that he knows where the exiles can find more slavers to take down.
Blackwire asks for more food and water to supply his people, he can pay it back with service and backup later.

Blackwire explains that three of his trusted underlings were captured by raiders and held for interrogation and execution when he defected. He would like the party to rescue the captured men from a slaver camp and return them safely, as they all know the location (and lock codes) of supply safes. On the plus side, he has at least one gang of former raiders ready to go right now. He can scrape together even more gangs of raiders if he just has time to call in the troopers - in the chaos of the raider army pulling back, some soldiers are deserting.

If the exiles rescue the three lieutenants, they can take at least half of the supply caches in the safes for themselves. At the very least, those three sub-commanders are tough and smart soldiers.