Boulder has a massive wave off the Contintial Divide. There have been flights above 30K ft when the Arapahoe Wave Window could be opened. Now when you call Center, they dont know what you are talking about. There has been an effort to reactive the wave window, but little progress.
One can still get very fast wave flights upto 17,999.
Mile High Gliding offers commercial tows to the rotor if you bring your own ship. They also rent an aluminum SGS 1-32 if you don't want to risk damaging the finish on your own glider.
If you like soaring cold and rough, come up to Boulder this winter.