EDIT: I SEARCHED AND SEE THAT YOU HAVE A SUBURBAN. DISREGARD THE INFO BELOW WHICH IS FOR A PICKUP. Looks like the part you need is a combo bolt and lockwasher (GM #3676478 in the Factory Asssembly Manual)
This is probably not the parts that you need, but just in case they are ...
The Truck Shop, 47-1101
clutch head bolts, nuts, washers kitThe Filling Station
Enter part number in "Search by part number" boxMK-48, Phillips head screw
GM-1254, Clutch head screw
TR-222, Clutch head bolts, nuts, washers kit
Classic Parts
Clutch head fender kitindividual clutch head bolts: 37-975
individual Phillips head bolts: 37-978
individual polished Phillips head bolts: 37-978P
individual stainless Phillips head bolts: 37-978S