The answer probably depends on what type of corruption he's seen and by whom. I'd try the office of RFK, Jr. You could also look up the frontline doctors group or the AAPS (at AAPS.org) to ask them for groups that can follow up on the issues appropriately. That's the medical watchdog route.

The other route would be media. Midwestern Doctor or Vigilant Fox seem like bloggers that could point you the right way. O'Keefe Media Group, Health Ranger, or Coffee & Covid might be other good media. I'd start slowly, making sure he trusts each step before outing himself. VPNs and temporary accounts are good ideas when beginning the process.