If you're willing to travel, I recommend the most famous US site -
Ridge Soaring in Julian, PA. Tom Knauff and Doris Grove have a great
reputation in the soaring community, and will set you safely on the
right course. And I can vouch from experience that you won't forget
any day get the chance to fly along the Appalachian ridges when the
wind is higher than 15 kt from 310!

-John