With the new movie coming out, probably everywhere! But there is a little store devoted to Pirate stuff, outsite off to the right when your exiting the POTC.
I am sure there will Pirate merchandise all over DL this summer. In general, there is a store at the exit of the POTC ride called Pieces of Eight where they always have Pirate merchandise.
Yes, Pirate stuff is everywhere in DL but not in DCA. We went in Jan and there was plenty of pirate merch!! There are pirate mickey ears for girls and guys. I got Captain Jack hair (wig) and there are tons of little trinkets- gold coins, the jail keys etc. World of Disney in DTD has a lot and and also stuff is scattered throughout DL. I wanted to buy it all but they are very expensive as usual!!
I'm at Disneyland right now and there is a ton of Pirate stuff! Jewelry, tshirts, Jack Sparrow roaming around the park, you will not be at a loss for pirate items. The pirate mickey ears are cool, they have a few different choices. If you buy a hat at the hat shop in California Adventure by the Mulholland Madness coaster they will embroider it for free. Here is a picture of my daughter with her mickey hat making a funny face.