I just called WDW Merchandise Mail Order Services and spoke with Deidre. She said that the hat and both shirts were exclusive to MouseGear at Epcot, and could not be ordered. She also said that the two retro shirts were not available at all at this time even in the store, and that MouseGear will be receiving a very limited order at the end of October with which to replenish their stock.
I'm pretty bummed out! I really want, if nothing else, one of those hats to wear when I am at Epcot on October 1st. Oh well...maybe I can unearth some other Epcot relic to wear and be special!