Where can I buy Jip's 'Y' T-shirt?

I'm furiously hunting for somewhere I can buy the blue 'Y' T-shirt that Jip wears to the Asylum in the film. It would be a momentously well-received surprise gift for my cousin who's birthday is next month but I can only find the 'Mr. Floppy' T-shirt or Koop's 'Junglist Movement' T-shirt.

If anyone can point me in the right direction it would be much appreciated.

Cheers,

Martin x