Yes - Starring Roles has grapefruit cake. If there's none in the display case, ask and they can get more. We were there last Tues and Starring Roles was closed so we went to the Brown Derby and were able to get some to go. We took it to eat while watching Indiana Jones.
This was my first time trying it - I have to say, I'm not sure what the hype is about. It wans't anything special and I wouldn't go out of my way to get it.
Apparently not everyone feels that way -I've heard it described as the best dessest at WDW. They even have the recipe on little cards they give out.