Soar Minden
Only one place worth going to in summertime, that would be "Soar Minden" near Reno, Nevada. Otherwise the US gliding scene is pretty patchy, as power operations tend to dominate. European type clubs scarce. Most gliding outfits in the USA are private enterprise, so not cheap, so you want to go for something special. I think you will probably find that something special in Nevada, near Reno, there are some really big mountains out there!... otherwise suggest Seminole gliding club in Florida in the wintertime instead, and have a seaplane ride at Jack Brown's which is not far from Seminole, at Winter Haven.
But if you have the time and the dosh, the holy grail of soaring flight has to be New Zealand!
Enjoy!