On this side of the pond they don't seem that common - or maybe I haven't looked hard enough...
Anyway the one site I have found pill boxes on is Magellans. In fact the site is full of overpriced items - the postage charge really kills...
They have been on my wishlist for months but I haven't been able to justify spending so much on so little..

http://magellans.co.uk/store/Health___Vitamin___Pill_OrganizersFV512?Args=