Not full sets or anything similar, that I am aware of. However, if you have the parts manual for your engine, you can order the bolts (technically referred to as screws) individually. You are better off buying your own grade 8s if you want something actually better than the stock Briggs bolts unless you just have to the stock ones and you can get the cool allen head ones that look really slick or regular hex heads. It's a common upgrade when hot rodding Briggs engines. There are full sets of spline head bolts for the Briggs engine by ARP but they are pretty darned expensive (like $65) and they only sell for the 5HP engines (as used in Jr. Dragsters).
I just checked on BASCO's (Briggs & Stratton Corp.) own site for the head bolts on a vintage 4HP engine: 93368 (Screw, Cylinder Head, 2 3/32" long) and 93369 (Screw, Cylinder Head, 2 15/32" long) and both say "Call Us" so they likely don't carry them anymore or they might tell you to just go to the hardware store too? lol Otherwise, I would just ask the members here if you absolutely need stock bolts for some reason (if you are missing some of yours or they are messed up or something).
*(5/15"x18tpi on the head bolts and 1/4"x20tpi on the intake/exhaust, are the Briggs' thread diameter and pitch on their bolts/screws)