just take the 12-pt socket head one down to your local hardware or parts store, it can be matched up with a hex head easily. I don't know the size off-hand. I swapped mine for 6-pt socket heads, makes putting the bolts back in easier, as the 6-pts hold onto an allen (hex key) wrench better to put the bolts back in.
there are other bolts around the car that can be substuted for better ones. One in particular is the flywheel-to crankshaft. The thin hex head bolts make taking the flywheel off a make-it or break-it situation. I have replaced the ones on all my cars with a regular, thick headed, hex bolt.