I don't think you're likely to find anyone here. We're a fairly small community and I'm not sure we have offensive security experts. It's also a little bit of a legal grey area, if not outright illegal. So, let's assume you're interested in doing perfectly legal penetration testing of systems that you are authorized to attack and probe for vulnerabilities. Anyway, I'm sure those communities are out there that can and will help, but I'd also be very wary of being used by them. Anon has done that plenty, teaching new "members" to be script kiddies and selling them up the river or not teaching them enough to know how to protect themselves.
But, there are two major parts of penetration testing. Vulnerability research and vulnerability exploitation. It sounds like you're more interested in the latter, which is fairly frowned upon, and doesn't often require deep security knowledge. You'd be testing the target system for published CVEs that likely already have patches to fix them and code to exploit them, so you'd just be running scripts and code that others wrote and checking if the target has the relevant patches to protect it from specific attacks. Not that that isn't a valid strategy, plenty of systems online remain out of date, unpatched, and unmonitored.
The other side, vulnerability research, is much harder and much more powerful. You'd be looking for these vulnerabilities yourself, which might require deep dives into code, smoke testing, etc, etc, and extensive knowledge on how systems are often run and configured. But, finding an all-new vulnerability means that it won't likely get patched for longer, sometimes much longer, unless the vulnerability is disclosed (white hat hacking). State actors (hackers hired by governments) are much more interested in these types of vulnerabilities.
Anyway, that's all I've got for you. I'm happily on the defensive side of security, so I can't help much. Good luck and keep yourself safe out there, if you continue to pursue this career.
