Most of the time, the Audio Forum is a welcoming place. You could discreetly look around there to see who looks agreeable and generous with their time:
https://www.newgrounds.com/bbs/forum/13
There may also be a Discord server related to aspiring NG audio artists, but as a Discord-hater I wouldn't know anything about that. (Why can't people just set up TeamSpeak servers?)
Yatsufusa
"Newgrounds is a community of people who are eager to help each other out. If you find someone whose music really clicks with you, Newgrounds makes it easy to reach out to them for feedback or general advice. So long as you're polite and respectful, people are often happy to help out an aspiring musician."
– anonymous musician on NG
More helpful stuff here (it's not much atm, but some of it might still help you):
https://www.newgrounds.com/collection/401376/guides-tutorials-for-musicians
thekingsqn
Thank you so much!!
We've been recording and making songs for years but only recently got the courage to post lmao. We're pretty confident instrumental-wise but hoping to get generally better at songwriting