They are called different things by different people, scrivets, plastic blind rivets, *insert body part here* retainer, push type rivet. They will usually have a size associated with them pertaining to the hole they fit into.
I couldn't find any suitable ones online anywhere so I went to the local Holden dealer this morning with the shroud which helped the parts guy find the correct ones using the shroud's part no. He was probably the friendliest / most helpful parts guy I have come across in a while. They didn't have any in stock (apparently there are only 15 of them in the state) so he has ordered four for me and will have them in on Monday.
Yeah, GM were always very original with their part names. It's always good to have the part number - it's amazing how many different versions of "scrivet" the manufacturers have come up with. And the bastards never seem to be interchangeable.....
Autobarn sell the exact right ones on their rotating fastener displays, $3.50 for four. I've had to replace a few lately. They are known generally as a push pin retainer, scrivets are the nickname given to their screw type counterparts, aka screw pin retainer.
