NASA retired theirs in the late '90's. There was a lady named Mary Schafer (sp?) who used to participate on Usenet who was pretty involved with NASA's SR program, and kept a running commentary on the program all the way through its end.
I'd bet my bottom dollar that they are *all* retired. It is easier and more PC to launch an RQ-170 or other stealthy platform to gather information instead of sending something that is non-stealthy and due to its sonic boom is a stick in the eye to the pride of the overflown countries.
Besides, the SR is vulnerable to the SA-5 and its derivatives, which are pretty widely fielded these days.