Bolt kits.

Keep in mind stainless does not have the strength of steel bolts.

Soak your greasy bolts in paint thinner for a couple of days, closed container.
Take out and let dry on a paper towel.
Rinse with brake cleaner, they will come clean.
If rusty sandblast, or soak in evaporust.
Regardless if you sandblast or soak in evaporust there must be no grease on them.