Moonbeams, IntheKnow is the most knowledgeable one around here regarding WDW bakeries and cakes. This person has mentioned frequently that we need to go through the Grand Floridian's Private Dining folks for any bakery requests. That was due to the high-volume of phone calls that they were getting. I'm not sure what the Grand Floridian's Private Dining phone number is anymore, but you can either search the boards for it or call the WDW Operator and ask to be transferred to it.
My guess is the same probably holds true of the other resorts on your list -- try contacting the resorts Room Service folks and place your order with them (if they cant take it, they will transfer you to someone who can).
I hope this helped. And I hope your cake is yummy.