So I removed my old grill, so that I can polish it out, and paint the brackets. The only problem is the old rivits were rounded on top and pressed from the under side of the rivit holding the grill to the brakcets. So my question is.... Do they make replcements for this, or do I just use regular rivits and rivit washers, or use machine screws and washers, or what?

Rod...get you some of these......

http://cgi.ebay.com/ebaymotors/64-65-66-67-68-Chevy-Chevelle-El-Camino-grille-rivets_W0QQcmdZViewItemQQcategoryZ33645QQihZ011QQi temZ320220081613QQrdZ1QQsspagenameZWDVW

Look and work great.

The machine screws are great if you want to take the grille apart in the future. You can also buy the round head, hollow rivets in aluminum or mild steel if you want to go that route (same source). In that case, you would use the correct punch or squeeze tool, not a blind rivet tool.