There were some test flights, but the drones weren't very reliable. I believe two were destroyed in crashes, and the rest are mothballed at Davis-Monthan.
http://www.me.mtu.edu/~slpost/nasa/
Photo's from Dryden of many of the vehicles in this thread: Be careful of your search spec in Google: several of the photo's of the SR-71/Y-12 drones on other sites were listed as D-12 (and M-12) - rather than the M/D-21 that should be used.