Just a thought
You have a CnC link above which leads to a page lacking the shirt. Put it on there with a say 5-10GBP (or equivalent) markup for the charity on it and see if it sells (it will). Make sure the donation part is spelt out and job's a good 'un.
There's no reason why a nifty design created for a bunch of Southerners doesn't sell up North as well and benefit all of humanity. Let's not get parochial here: MS is a dreadful disease wherever you are from and any well conceived initiative to raise funds for combatting it, regardless of where they are spent (hopefully collaboratively), is a good thing.