I bought mine at home depot. The bolts that hold the Razor quad wheels on are M8 X 1.25. They have hex head up to 65mm I think. They did not have any allen head. The hardware store has a better selection but they cost more.
Rob you know how to deal with all thread right? You put a nut or two on it before you cut it so you can screw the nut off of the cut end and straighten out the threads. You probably know this already but I was just making sure.