Triumph release their sales figures every year, so it shouldn't be too hard to find out. They'll probably even tell you themselves, if you emailed the
PR dept.
I believe that sales have been increasing every year, so they should have shifted a few by now, especially if you include all the variants (Thrux, Scram, T100, Speedy & American)
But as they're still being made, I don't think now's the right time to be doing the tally up. For as Kenny Rodgers wisely observed, "There'll be time enough for counting, when the dealing's done."