If they are one size I see listed online they are 8mm x 55mm long, but they don't list the thread pitch. I would guess 1.25 (medium coarse) Bring your old one to any hardware or auto parts store....metric studs are fairly universal, you don't even need extra strong grade 8 bolts, grade 5 will do just fine.
If you've got one of the double sized ones...like this....
http://www.ebay.com/itm/Honda-CB750-F-DOHC-79-Exhaust-Studs-Nuts-Pair-/150514651452#vi-descYou're probably only going to find those at a motorcycle shop, or special ordering them.
Mark Davis
Palm Beach Gardens, FL
amateur photographer, hot rodder, motorcyclist, adventurer
"Four wheels move the body. Two wheels move the soul."