Search the forum for that part number, and I'm sure you'll find quite a few threads on the subject. Online is probably best, as long as you buy large enough quantities to justify the shipping charge. I think going rate online is about $4 each (before shipping). They're $5.50 at my dealer before a 10% discount for buying the truck there.
I checked ebay and found them in one of the stores. Koons Arlington Toyota had them. I just put "YZZD3" into the search engine and it was the third option that came up.