Find where bands post listing looking for musicians.
Craiglist is the easiest one, but can also be the most frustrating because anyone can post there, serious or not.
Pre-internet, it was all about local music magazines.
There is a site called Musician Contact Service. You have to pay to join, but because it is a pay site, ads tend to be much more serious than what's on Craigslist.
Of course, nothing beats world of mouth.