Um ... wrong: IKEA's owners DO also own HABITAT - though it might be that the UK stores are still independent but I doubt that: Quote from business section of a Swedish Newspaper. "The family of Ingvar Kamprad, the Swedish billionaire founder of the Ikea discount furniture chain, is thinking about ditching the high-end Habitat furniture and design chain." ... interesting definition of "high-end"...
As a design manager from that business area I am absolutely sure about 2 things: IKEA and Habitat DO source from the same Far East suppliers - simply because Habitat's sales are way too small to get decent conditions (= low prices). They HAVE to enter their purchasing talks with an opening line like "We, Habitat, part of the mighty Ikea brand demand you to give us a decent price..." - that's just the way you do it.
Secondly, from a brand perspective, it would be very stupid if IKEA sold identical products under both brands.
So I think we are simply out of luck when it comes to finding those Tzaria cups... and maybe that's good. As much as I love the design, the quality was appalling: I showed some Tzaria pieces to a designer from a big (EU) china manufacturer. Her response was "they SELL these??? - this is stuff we would throw in the dumpster right away" (90% of the pieces I have a actually warped or have glazing errors - plus, Tzaria chips easily which indicates that they have taken some manufacturing shortcuts to save money)