Looking for Ayu t-shirts?

It's my 16th birthday on April 1st and my mum asked me if there was something I really wanted. And yes, i'm really interested in an Ayumi shirt. I've yet to have the oppotunity to buy one and now seems the perfect chance because i'm also going to London for a trip and I would love to wear it there.
Is there anywhere that seels Ayumi t-shirts. Yes I know there is ebay but any buyers a side from ayumi showcase. His prices are like crazy haha.
So a little help please? ^.^