It's also available in International sections of a couple grocery stores (or in grocery stores that are known for being international or at least having that fancy pants sorts of stuff)....
For instance, there is an equivalent of that used as part of a sweet in India and Pakistan.. though, how that would be written in english letters, I do not know...
bottom line, check out the international section of the grocery store and see if something says "clotted cream" or some such thing on the packaging or as the main/sole ingredient...
(though, as someone else suggested, a tea store may be your most _direct_ bet if you can find one locally).