It was more than we needed. We thought it would be so nice to have someone show the guests a few steps of an Irish jig or a May dance or something. We ended up taping our favorite songs from our collection of celtic CDs and piping it through the ballroom's sound system. The music was played on a small tape machine hidden out of sight. Contact them and ask if they have a group that performs.
People often know people who know people.
Through the staff at the Renaissance Faire where we held our wedding, we hired a woman that played hammered dulcimer. Since the demand for Ren music is small, their prices tend to be low. You might try seeing if there's a local English Country Dance or Contra Dance community in your area. Word of mouth is the best way to find a band or anything else for that matter. Ask couples or parents who have recently had a wedding.