Sorry if this is against the rules, I don't post on the music board often, or ever really, but this seemed like the best place to ask. Is there any kind of message board or website or forum that exists at least partially for the purpose of advertising live shows?
None that I'm aware of, maybe some local musician Facebook groups
If you're in a band and have an account on certain sites like a nation of reverb, or a camp for bands, one can post announcement for shows there, otherwise face book is a good place.
There are probably some forum sites where you could do this as well, especially if they discuss local music.