I have M6 (6mm diameter) 50mm and 60 mm bolts for $2.89 each and FREE shipping, links for both sizes below;
50mm Minelab Sovereign GT Elite Nylon Bolt Wing Nut Coils Arm Cuff Mounting | eBay
Minelab Sovereign GT Elite 60mm Nylon Bolt Wing Nut Coils Arm Cuff Mounting | eBay
These will work...