Years back I heard about such fast track vouchers for sale and out of curiosity I searched high and low see if I could get a hand on some to try and see if it is for real. However, all the sellers I had come across were bogus and more like a scam.
Fast track voucher for sale might be true years ago, but might just be some inside staff steal a bunch out (the one I saw being sold online was the whole book of voucher), since back then the vouchers were hardly changed and some real ones weren't even printed with airline stamp and departure date so it could easily be reused too. Doubt so now though.