My son is starting to play trumpet and he has is trying to play He's a pirate by ear and it's not bad, but I would like to find the sheet music for him so he can perfect it. Could someone help me please?

If you play the clarinet, trumpet or trombone, alto saxophone or tenor saxophone you can purchase and download the accompaniment part for your instrument.
Full version of the party and the accompaniment are in a RAR format.
http://www.brassminus.com

You're not going to find it for free. You're going to have to buy the book of PoC songs (it's really good by the way). $12.50 from Sheet Music Plus.