You can buy the lug bolts from the dealer parts counter. They come with a corrosion-resistant finish, but that doesn't mean corrosion-proof over time. If you want to give them an extra dose of protection, get some silver spray paint (or other color, perhaps to match your wheels if they're black or gunmetal?) and spray a couple of coats. Just be sure to mask off the ball seat and threads before you do so. And be aware that going this route will mean that you'll have to touch up the lug bolts occasionally, since any socket used to spin them out to remove the wheel will likely scratch them.