The true STR-1, with the under the bottom bracket tubing, that "cradles" the bottom bracket never was a production bike. A number of team riders probably rode one for testing and feedback purposes. There are only 2 existing STR-1 frames known.
Note: Some people insist that what we know as the earliest loop tail quad was also an STR-1, even without the under the bb tubing. Some people also assert that there were quadangles out in 79 - beyond team riders, there is no objective evidence that is actually the case.
Below are photos of the actual STR-1's known to the community. The first one was this one:
and the more recent one that surfaced a couple years ago is this one: