There are two types/sizes. I got a package of each type from ebay, total about $10. It's probably a good idea to get a bunch because I broke them really easily. Just search ebay for these part numbers:

91501-S04-003
91503-SZ3-003

 

When I needed these I just went to the local Fastenal store and bought a bag of Honda clips and a bag of Ford clips. I use the Ford clips where I do not need the flush fit. The head of the push pin protrudes a little on the ford clip and it is easier to pull them.