XB-70 is out of service. The components that was to be flying with it should be dead as well.
The components, yes, the technology, no. The Air Force and NASA put a lot of time and money into what would have eventually become either a single- or two-stage to orbit aircraft/spacecraft. I don't know if you have heard of the X-15 or the
NF-104 programs, but we were within probably 10 years of having their successors operational (and orbital) if it weren't for Vietnam, according to pilots I've spoken with in the '70s when I entered the AF, as well as my father who was at Edwards AFB in the '50s and '60s.
Unfortunately, Vietnam took more and more of the federal budget, and Johnson or Nixon or somebody below them decided that we were spending enough on the Apollo missions as it was.
I've never looked it up to see specifics, but Burt Rutan was with the Air Force at Edwards - maybe that's where the inspiration for SpaceShip One came from (the X-15 program).
Regardless, we had the technology to fly into and out of space from a horizontal takeoff (even if it was a two-ship combo) going back to the '60s (and you could argue late '50s), but the money wasn't there. It would have been a lot cheaper than the Space Shuttle (then again, because of the massive amounts of money sucked up by large projects like the Shuttle that go on for decades, I could see the aerospace companies lobbying against cheaper/smaller spacecraft in favor of larger do-it-all spacecraft).
In other words, this wouldn't surprise me - the AF had no problems with the SR-71 being mothballed, and publicly they and NASA have done a lot of very high-performance engine testing over the past few decades.