Broken Bolt

You know you need to be more specific. Are you replacing a cylinder head bolt? Many of those are "torque-to-yield" bolts that are designed to stretch as they're tightened. Those are one-time-use and must be replaced every time they're removed.

Are you working on the suspension system? A lot of times those are treated for corrosion resistance. Same with the bolts that hold on stiffening plates under some engine cross members.

Bolts in the steering and suspension systems are of a minimum grade for hardness. The cheaper hardware store bolts must not be used in these applications. Hardware stores, farm and home stores, and auto parts stores all will have grade 5 or grade 8 bolts, and they don't cost that much more than the cheap ones.

Any bolt you need can be found in a salvage yard, but if it's for a safety-related system or you need the special corrosion protection, or it's a one-time-use bolt, you can find them, usually in stock, at the dealer's parts department.