Belarusians, Russians Join Ukraine’s Military
wsj.com
wsj.com
https://twitter.com/KofmanMichael
Like the other commenter said, these are part of OSINT (open source intelligence) twitter.
Outside of twitter this is a good start: https://www.oryxspioenkop.com/
Maybe reach out to Ukrainian leaders on what they'd like them to do, etc... It's highly risky sure, but no more risky than fighting from Ukraine for Ukraine...