A site i use to use to get some acapellas from was
http://www.acapellas4u.co.uk they did take them all down due to legal action being taken against them, but i think now they are all back up
here is a list of the acapellas that they have ........
http://www.acapellas4u.co.uk/lists/acapellas4u_list.txt
hope it helps for budding producers out