I'm from the states but have been in the UK for nearly 5 years and I can't tell you how much I miss my fabric shops. It's horrible here, I have to take a chance and order online. Not easy when you're a touchy geeky person.
I stock up big time when I fly over and my mom is bringing quite a bit back with her. The only bad part of that now is that even on international flights, you have to pay $50 for a second checked bag now.
On a positive note, it is still cheaper to buy fabric overseas even with the postage, tax, and our lovely handling fee from parcel force... If it gets posted by the other big brand couriers then their fees aren't as high but their postage is higher. The best time to buy is spring and summer time as that is when the exchange rates are usually the best. I base my exchange on travelex but paypal will give a slightly better rate, just easier to get an idea from travelex. Just keep your value down and you will avoid both tax rates.