This stuff is extremely hard to find. We have been trying to track it down for several weeks now. One place was expecting their shipment in on November 7. The Geek and I stopped by on the 8th and the store was closed until November 18. I suspect they got their order and promptly scalped all the tubes, enabling them to go on the first of many exotic winter vacations.
Another tile company (which is now on my list of unorganized, and therefore untrustworthy, businesses) took my name twice and promised to advise me when the Kerdi-fix came in. They didn't and The Geek just happened to call today and bought their last tube. They were the only two retailers in town.
But, it has been bought, and applied and that is all that matters!