I looked up the part numbers of those 4 grill trim pieces, they are C6GY-8419-C, C6GY-8419-D, C6GY-8419-E, C6GY-8419-F, depending on if they are top or bottom, and right or left. Originally they came with the special clips, and they are part number C6GY-8A072-C, but the clips were available separately. Looks like each piece of trim took 3 clips. I did a quick Google search, it looks like the trim turns up for sale on eBay periodically. You could try searching those part numbers and see if you find anything. I would try calling some of the various NOS parts places, like Green Sales, always a chance they have some. As you've found though, probably a hard part to find since it's a one year ( 1966 ) only and one vehicle ( Comet ) only part. Hopefully someone maybe has come up with a homemade solution for you, or has some extra clips from a parts car. I don't know if you're on Facebook, but there is a group for Comet fans, you could try a wanted appeal there too. Good luck Jim.