If you’re not already using Meetup.com to build connections, I thoroughly recommend giving it a shot.
How do I find the right members for my Meetup Group?
My current Meetup is for small concerts and house concerts… I know other people like house concerts. Now, how on earth do I find them?
Melissa, Organizer Brisbane Bookclub; The House of Owls: Make a little card or flyer to hand out at the next house concert you attend, or advertise your meetup at the venue with posters.
Shella, Organizer History Reading Circle-SF: I might try reaching out to other Meetup Organizers to see if they would cross-post your events. And try circulating flyers at book stores, music stores, music events, etc.
Lana, Organizer in Walnut Creek, CA: Perhaps send the Organizer of a similar group an email asking her for advice? Another option is to look into the local musicians union.
Source: Meetup Organizers’ Forum