Not constantly, just presently. After the next production run, they will be abundant.
Rarely sold sizes are made in limited runs, maybe once or twice a year. The manufacturers try not to build more than they can sell quickly, as buyers are now aware of date codes and will refuse "old" tires.
Try other brands, or be willing to accept the tire you want at any age that can be found. There are usually a few tires somewhere, warehouse or another dealer's stock, but most tire dealers won't try very hard if they have something else to sell you.
