I thought I had logged into the Hampton Bay ceiling fan site and this was the only way I could get help. I'll go ahead with my question which is -
How can I order from the company the 12" extension that belongs with the "Designer Edition" ceiling fan called "Easy Street", Model 134674? Can someone give me a telephone number or email address to contact the parts department for the company?

They should sell that at Home Depot. Was it supposed to be included with the fan?

Yep they do carry them at HD but the 12" isn't part of the package, it is an accessory.