I am uncertain if anybody on these forums has a spare Ninja Pig code. As you said, they are really rare (I was incredibly fortunate to get one myself), and I do not suspect anyone here has a spare code in their possession.
However, it is entirely possible that Kingsisle may run Ninja Pig promotions again sometime in the future. If they are listening to this, it would be a great way to bring players back to this game.
They occasionally make a comeback for specials and other rare events... but yes, rarely.
This is just a recommendation, but might I suggest thinking about having a Ninja Pig giveaway at Kingsisle's next Pirate101 event? It's been a couple of years since this companion was last made available, and I'm sure newer players would love the change to obtain the Ninja Pig.