The Thomson web site only lists 25.4 in the Elite style, and 3.18 in the Elite x2 & x4.
So, yes, I'd guess the 26.0 is no longer in production. They were only making limited sizes of 26.0 stems and only in black recently, so it was probably being phased out.
Try ebay I suppose? Or just ask around at shops, I've found some good new old stock stuff that has just be sitting on the shelf.