My wife and I were discussing this because we take loose tea to friends abroad who similarly dislike teabags. She was in ASDA today and says they still have it under their own brand. Tesco probably also still have it. Additionally, "bespoke" coffee and tea shops, such as the one near us, definitely have it but at a significantly higher price. Finally, I know of a Pakistani owned shop (also fairly near us) which not long ago had quite large bags of loose black tea for sale (Indian owned shops quite possibly also) but I have not been there for a while.