I live near Saint John, New Brunswick too!!! I wish I had a good answer to your question as I have also fallen in love with many designer fabrics since discovering Sew Mama Sew (if there were no such thing as customs and duty taxes I would have placed many orders by now!)

I have found a few on-line sources through an internet search, but haven't ordered from any of them yet so I can't tell you what they are like. They are:
http://www.hamelsfabrics.com/ They have both Amy Butler and Michael Miller fabrics
Then there is this list:
http://www.chebucto.ns.ca/~ae862/mailorder.htmlIf you go on the Amy Butler website
http://www.amybutlerdesign.com/buy/ there is a list of stores, and if you click on find a shop in your area and then click on Canada, there is a list of Canadian shops and some have mail-order (the farthest East store is in Montreal, so no luck in finding anything in Atlantic Canada!)
Ebay also has lots of listings for these fabrics, but again they are usually being sent from the U.S.
A little closer to home, Town & Country Quilts in Rothesay is supplied by a company that carries Michael Miller - I don't know if they regularly carry any of his line or not, but it might be worth a phone call.
Good luck! I'd be interested in knowing if anyone has ordered from any of these places and what they are like! If you only want a small amount of fabric, you can order up to $20 from the United States without having to pay duty on it. Even with the exchange on the dollar, most of these fabrics cost less across the border.
Hope that helps!