I second the suggestion of Instagram as far as social media platforms go. Because it’s visual, you’ll reach the people who are looking for visual art. I follow visual artists on there so that I can find them again when I want to commission character art, and I’m sure I’m not the only one. So Instagram is a good place to connect with people.
As far as where to post commissions, I’ve seen people do that through DeviantArt before, or Ko-fi (the latter of which is not visual arts-specific, but can be used by artists of any stripe. Nate Philbrick and Svenja are a couple of artists I follow there, and the forum won’t let me post this with both links so here’s just one and I’ll add the other in a separate post).
Speculative fiction author. Mythology nerd. Worldbuilding enthusiast. Singer. Fan of classic literature.