We first discussed Vulnerability Lab, like Hackerone, in the context of good bug bounty researcher communities. In addition to being a great source for discovering new bounty programs, Vulnerability Lab also maintains an archive (https://www.vulnerability-lab.com/) of all the bug reports submitted on its platform (whose program owners also agree to publicly disclosing the vulnerability):
One of the most valuable elements of the Vulnerability Lab archive is that each report is organized by type—whether it's a web application, mobile app, or general vendor vulnerability—making it easy to drill down into the reports that are most relevant to your practice.