I don't think they are on sale yet. Took a look at the TRD site and all I could find were oil caps, filters, and air box top. I'm guessing they've released the renderings of their kits only and haven't actually put them up for sale yet.
If they are a TRD product, it'll be a dealership order that they may have in stock in Japan. Best bet is to call the parts department and ask them if they can give you an estimated time on when they will be getting them or if you can order them in.
In regards to gas mileage, I haven't heard of anyone noticing a difference at all due to mudflaps.