Hesston 1007 mower

I'm gonna need to change out my knives on my 1007 disc mower. Looks like the little shield that I guess protects the bolt has gotten wore down over time on some of the rotors and the bolt heads are rounded off. What's the best way to get these rounded heads off and can you still buy that little protector. Got all new hardware and the blades but don't have the little protector. Thanks

Hesston 1007 mower