Jim,
Woodland pattern battle dress uniforms (BDUs) were phased out by the Army years ago, but the U.S. Air Force has allowed their personnel to wear them longer, even as they transitioned to other camo pattern uniforms. Final BDU phase out for the Air Force is reported to be November 1st, 2011, so the availability of this used gear will continue to taper off, even in base thrift stores.
Note that with two forms of identification, most Americans can access a base to visit a thrift store. Military base thrift stores are usually operated as private, charitable organizations and have limited hours and days. – W.J.