They are M6 20mm and I'm almost certain they are the same as the R6/R1 bolts.
The MT-03 set from Pro-Bolt fit the XTZ and you'll find the part numbers the same as R1/R6. Wemoto sell them too, but they are exactly the same product and price as Pro-Bolt.
http://www.pro-bolt.com/index.php/st...l#.T5Qp7yKF9iE