Yes, I know you don't have any. I'm not blind. For those of you who are blind or seeing-impaired or whatever, the Island is clothing-optional. Some people, though, are rather shy. If you are reading this, I gather you are one of them, so, yes, I know you want some. Tough. You can't buy them, and unless you pants somebody who has a pair, you'll have to find them on your own.
Pants are found in the Jungle or during Travel. They are a medium-difficult opponent,1) so don't expect to come across them right away. If you defeat them without damaging them too badly2), you can be decently clad once more.3)