Wal-Mart or the Spirit Halloween store would be one of your best bets. You could also try something like: http://www.costumeholidayhouse.com/deluxe_costumes/all-deluxe.asp
If you visit www.costumecraze.com you can find the traditional pirate costume you may be looking for. You can also visit www.partycity.com for a non-traditional pirate costume.
Usually at Halloween pirate costumes are easy to purchase at any costume store. If it is not Halloween there are many used stores that will help a person find a used costume.
Cosplaytrader.com is a good start! Alright you can make a costume or go to the good will and find a nice costume or you can find some clothes that would go with you costume a kid i know did that and went as a pirate!
go to the fancy dress shop and get a pirate costume
I always go for an all-out costume and for this, I'd suggest http://www.elizabethan-era.org.uk/pirate-flags.htm They have a accurate selection of real pirate flags.
it's only for poptropica members but you can find other pirate costumes on the differant islands
pee in a cup
A Pirate
A pirate costume should have both a sword and an eye patch. If you can only do one, you should definitely do an eye patch. Make sure to also have a pirates hat to complete the costume.
Costume supply outlets carry them.
nothing just for decoration
Anything that is to do with a pirate. For example, when we did the play, we ha d a pirate costume complete with an eyepatch and a hook. This will help with what the other pirates have to wear...