When did you live in Budapest ?
The Clinton years. Somewhat of an exile, you might say.
I remember supping on nice karalbe leves and also cooking toltot karalbe, stuffed with a beef/onion/spice mixture. It was a favorite meal for this time of year. The Danes use kohlrabi for cow fodder; they told me it is not for human consumption there. Hmmm. They don't know what they are missing.
I shall have to go out looking for it.
I don't know where you live ; however , I do know that you can find the elusive Karalabe in Conn., N.Y.C., and Chicago. You may have missed the " season ", though. Good luck in your hunt.