McSpadden doesn't show any pictures so it's hard to be sure they're advertising what you want, and I don't find anything at Fender that looks promising.

Andy's Front Hall does have a picture of the triangular one with a bunch of D'ADDARIO FLAT PICKS. The brown one is the one in question. The picture doesn't say the triangular one is a D'ADDARIO, although it might be(?). It's described only as a "LARGE TRIANGLE FLATPICK
Shell A/MA 355   Thin: $.30 Medium: $.40"

The only "identity" I found at "Andy's" was a 'phone number, but a lookup on it shows:

Andys Front Hall Books & Music
Wormer Rd
Voorheesville, NY
(518) 765-4193

Other info on Andys gives the impression he's a "local shop with a computer," so there'd be little incentive to order there if a shop in your own neighborhood can get them for you. With a print of what it looks like, I would think that any local music shop should be able to find it in their wholesale catalogs and would be able to get you a hand full. Unfortunately common guitar picks are also called "large triangle flatpicks" and most definitely are NOT what you want.

John