While there are plenty of "8" pneumatic wheels" still out there, the OP does have a point regarding 200x50mm tires, specifically. The stock levels usually maintained by various vendors of these tires is not sufficient to meet the additional demands placed by FRC on the market. This is not really a manufacturer issue*, but rather an issue for the vendors selling replacement tubes/tires directly to consumers.
If you take a quick look around, you'll notice quite a few vendors listing 200x50 as out of stock, low stock, or back ordered. Sheng Chin and Primo tires, in particular, are running out just about everywhere.
http://www.mfgsupply.com/8-10428.html
http://enableyourlife.com/8-2-in-200...otrap-tire.asp
http://www.amazon.com/gp/product/B00...=sr_1_2&sr=8-2
http://www.amazon.com/s/ref=nb_sb_no...s=primo+200x50
Granted, there are still vendors out there who have these tires. This is especially true if you're willing to accept ones that are foam-filled, "flat-free" (solid rubber), or are marring. This isn't an apocalypse for the communities that normally need these tires, but it has certainly made an impact.
*Manufacturers are going to be ordering in bulk from the factory or places like alibaba, and are not expecting quick turnarounds.