Update: Wasn't as lucky with the "rivets" or "push-pins". I ordered 5mm push-pins because that's how they were listed on G1parts, but it appears I need larger ones, probably 6.5mm or 7mm. The "rivets" are close, but it appears they're designed to go on thicker trim pieces and thus are a bit loose.
EDIT: I believe these are what I need to order:
http://www.ebay.com/itm/50PCS-7mm-Ho...e24d0d&vxp=mtr
http://www.ebay.com/itm/371137780922