Lowe's and Home Depot carry most common automotive fasteners in drawers in the hardware aisle, probably your best bet.
Otherwise, if you want to go to the dealer, have him pull up section 640 in FAST and he'll find the part numbers. There are 2 different clips shown holding that rubber flap (Cover - splash, hoodledge) and I'm not sure which you need. Based on your description I'd go with 76876-S3800 though.

Brent
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