In the USA I have bought from these sellers with success: (I am in NY, FYI)
K&L Wines:
http://www.klwines.com/
Park Ave Liquor Shop:
http://www.parkaveliquor.com/
Ultimate Wine Shop:
http://www.ultimatewineshop.com/
Binny's Beverage Depot:
http://www.binnys.com/
I've had stuff shipped from all of the above (except Park Ave, which couriers it to me for free in Manhattan with a > $50 order)
I hope this helps.
Dan