did you happen to ask at Guest Services or a mousekeeper? I'm guessing most hairdryers come with diffusers so I wonder if possibly they have a stock for people who request them?
I am constantly amazed at what Disney does carry/offer when I ask. I use a CPAP machine and it's nice to know distilled water is available in the food court even though most times I take my own.
Also, my daughter is extremely sensitive to many detergents so I normally travel with either our own sheets or a special sheet made into a sleeping bag kind of thing that she can sleep in. One time I forgot to bring both and I was pleasantly surprised to find out I can request hypoallergenic sheets and towels for our room! SO much easier!
This hypoallergenic request is awesome! When did you make the request? At check in?