Crowd source funds and hire private investigators.

You'll instantly have an army of boots on the ground. This will also have a powerful psychological effect on the people you're investigating. They'll know there's a army of professionals up their assess. Even the ones that aren't being investigated will be sweating. Trust me, all you guys gotta to is crowd source cash and hire PIs. That's all it will take for you guys to become an actual legit private intelligence agency.

The only thing you'll have to do is watch out for misinformation being funnelled to you by double agents ( sellout private investigators). The best way to do this would be to selectively hire PIs as well as to set up a small group of PIs that investigate the main body of agents.

You'll essentially need to form a group of private investigators to investigate your private investigators.

Anyways, I'm not going to go into detail and explain how all this should be accomplished, but it's really simple.

Crowd source funds and hire private investigators, and then hire a few more private investigators to investigate the others.

You guys will want to probably remain anonymous and decentralized. Don't give your organization a head for them to cut off. Keep everybody compartmentalized.

Just crowd source money and hire private investigators and make all their reports publicly accessible.