I am looking for a repository of real life vulnerabilities (in this specific situation, buffer overflows in C & C++) that have been detected in open source software. Ideally it would show exactly where in the code the vulnerabilities have occurred in the past, and how it was patched (if it is patched).
Try this one (https://blogs.securiteam.com/index.php/archives/2543#more-2543), the advisory shows the vulnerable code and since it's an open source product the patch is available from the vendor source code (http://www.live555.com/liveMedia/public/).
Check out exploitdb by Offensive Security: https://www.exploit-db.com/
Rapid7 is also a great place. You can try to run a granular google search there.
Most of the time you'll see great examples of vulnerabilities and threats along with where to find hotfixes for them.