The stainless capped bolts are available from a variety of suppliers. You want to make sure you get ones with "low profile" heads as opposed to standard carriage bolts that have a more pronounced head. Here's a link for some for sale on Ebay.
http://www.ebay.com/itm/GM-Camaro-Fi...318ef6&vxp=mtr
Here's another link that has the flanged nuts with serrations.
http://www.ebay.com/itm/GM-Bumper-Bo...783dc2&vxp=mtr