Julia,
Have you heard of Blue Lake Fine Arts Camp? They have a wonderful harp program for harpists of all skill levels with opportunities to work on solo music and play in harp ensembles. I went to Blue Lake as a camper for 3 summer sessions, and this past summer I worked as the harp assistant/counselor. It was a great experience both as a camper and as a counselor.
The camp is in Twin Lakes, Michigan and each session is 12 days long. Being a harp major at Blue Lake is a lot of hard work, but it is a great experience!
Good luck!
~Stefanie