This happened at a wedding I attended in Missouri, which featured the musical stylings of the bride's second cousin. The poor girl's sole qualifications were membership in her high school choir, and an overwhelming desire to be in the wedding. But she had never sung a solo before. There's a Kodak moment. If you have a more easy-going pastor, but still don't know any good musicians, call local music stores.
Chances are, the person answering the phone either is a good musician, or knows someone who is.
Many music stores also have business cards of professional musicians tacked to bulletin boards. Do not assign me a seat at the reception next to Mr. and Mrs. Let me choose where and with whom to sit. Have your wedding in the early evening, with reception to follow. Keep close tabs on the groomsmen.