Linked here so I don't have to waste a lot of time looking for what I already found once:
Buckeye Dulcimer Festival, Ashley, Ohio, March 10 - 14. http://www.buckeyedulcimerfestival.com/
Yellowbanks Dulcimer Festival, Owensboro, Ky., June 5-6. http://www.kyfestivals.com/details.php?id=591
Gateway Dulcimer Music Festival, Belleville, Aug. 13-15. http://www.gatewaydulcimer.org/
August Dulcimer Daze, Friday, Aug. 14-Sunday, Aug. 16, West Dover, Vt. Workshops by George Haggerty, Lorraine and Bennet Hammond, Mike Anderson - some theory and technique that sounds good, almost entirely in DAD, tho'.