Clarity might be a good point to start if you search for "social impact mentor" https://clarity.fm/search/social%20impact

Otherwise, there are a number of platforms out there, the best approach would be to research on Google based on your specific needs and geographical location.

Facebook also runs a social impact mentoring platform https://socialimpact.facebook.com/mentorship/ for Facebook groups focusing on social impact so it could be worthwhile also searching on Facebook for relevant groups.

Good luck!

Clarity is the best place to look for expert of any type, but if you still believe you want something more you can try this link: https://www.global-changemakers.net/mentorship
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath