I heard that VitaTreat carrots are the best carrots, but I cannot find them in any seed catalogue. Does anyone know where to buy seed for this type of carrot?

I agree that it is hard to find.
It is a hybrid that was created by Seminis in 1998.
Seminis is a corporate supplier of seeds to big farm operations. They do sell directly to gardeners.
Some of their seeds do make there way to home gardener catalogs, but I can't find Vita-Treat available with any seed company that is searchable on the web.