Bone Suckin' Sauce seems to be quite highly regarded in the US (from what I've seen looking at reviews online).
I've found it for sale in two places in the UK, both offer mail order options.
http://www.bbq.co.uk/acatalog/bone-suckin-original-sauce.html
http://www.americansweets.co.uk/usa-rated-1-bone-suckin-sauces-130-c.asp
Note: At the time of posting American Sweets are out of stock but are expecting to get it in 4 weeks time. They are also looking into importing Blueshog!!!!!!