This is where i get mine from,
http://www.apmex.com/Category/257/Todays_Wholesale_Lots_SILVER.aspx
It's a good silver wholesaler but you need an address in the US. A mate of mine is married to an American Girl so they go back a few times a year, I get it sent to Her mothers Place and they bring it back for me.
I'm sure it would not be that hard to work something else out.
Also ebay Is great for cheap silver but watch the postage.