I don't think they exist. Or at least I didn't until recently. Stanza , over at cookingonsundays, has a typically eyebrow raising recipe up this week, which includes a cabbage so large, well, I can't really say since it seems to change size throughout the story, but I'm certain it is bigger than a teapot!
I too found a V.O.U.S. this year. It was a giant mangle beet from a farmers market. It only cost me a few bucks, and it was around 18 pounds! You can see Kernal subduing it for me in the above picture. I did a bit of research, and apparently mangle beets are grown mostly as fodder for animals like cattle, but are quite edible. After carrying it home on my shoulder like some prehistoric vegetarian, I chopped it into three pieces. The bottom I juiced and froze in ziplocks for future soup base. The middle I gave to the chickens, who happily stood inside it and hollowed it out. The top I planted, in the hopes that it would grow into a new beet next year. So far, so good.