Bilstein Upside Down are racecar specific parts. But Alpina and a few others used them also for street cars, but not with unibal.
The rear Bilstein Upside Down you can buy new at every dealer (in germany, I do not know in the US). The front shocks you can also buy new at Bilstein Motorsport, but you also need the special strut. In my opinion, repairing Upside Down parts makes only sense if they have 11mm rods and not the old 10,5mm.