Do you mean a complete hubset, or just the QR skewer?? If you just need a QR skewer I wonder if you can't just take a 130mm one and screw it down a few more revolutions. If not, I imagine there are plenty of used ones on ebay. If you want a complete rear hubset at 126mm your best bet is NOS also on ebay (that is what I did for my new 126mm rear wheel).