Can be a bit tricky getting hold of some bolts in aircraft grade stainless and 'normal' stainless bolts can be weak compared to high tensile carbon steel.
But not every application needs them, and yours sounds like it doesn't and normal stainless steel would be fine.
What do the bolts go into, and how tight are they? If not super tight you ought to be fine with stainless. You could try asking the dealer, a torque figure will give the game away as to the bolt type needed.
Production wise - I've never met a car manufacturer that routinely used stainless, it's an expensive choice and most engines are under bonnets.
Don't bother painting, it's hard to do a good job, and the paint will either fall off or obstruct a spanner at removal time. (And given my sort of luck - both would be a possibility!)
