FWIW, this is the default broccoli in center italy (hence the name "romanesco"[0]). Took me decades to understand why american media used such weird broccoli (i.e. what the rest of the world call thus).
I've always wondered if those are the ones in the famous Diocletian quote "Would you could see the cabbages planted by my hand at Salona, you would then never think of urging such an attempt [to return from retirement as Emperor]".
Another plant he left out was Arabidopsis, which is the model organism most studied by plant biologists as it has the second shortest plant genome (they used to think it was the shortest). My company (http://www.glowingplant.com) is engineering these to make them glow in the dark... so maybe we can make glow-in-the-dark broccoli next ;) It's not hundreds of years to make new cultivars now, dramatic changes can be achieved in months. Fun fact: you can make an arabidopsis look like a Brussels sprout with the modification to a single gene... it wouldn't taste as good though, that takes more genes!
You can make them at home, but it requires a lot of work and luck, since brassicas cross-breed if they are near each other at all.