Does anyone know where I could find some replacement rear hub bolts for a Sierra? I've managed to grind the end of one when I was removing. The thread is 10mm x 50mm.

They are not special bolts so you could just source them pretty much anywhere, E Bay will certainly have them but you will need to know the pitch, looks like 1.25mm, I would suggest a 10.9 strength bolt.

The Haynes manual has some notes about these bolts. There are two different sorts. I attach a snippet from the manual. Yours look like Type Y bolts which are the higher tensile bolts 80 - 100 Nm on torque.