Now that it is fall, I thought I would resurrect this question. Russo's today said they would have them for the holidays. Has anyone seen them anywhere else?
Arax in Watertown has them some times, I would call and ask. Likewise, bet you could get them at Russo's or the greengrover on Prince Street in the North End. In all those locals they are only a "sometimes" item.
Cardoons are usually a fall crop, so I have been surprised to see them quite regularly at Russo's over the past few weeks. My most recent cardoon sighting there was yesterday.
Oh, and for some reason the tag on the cardoons at Russo's says they are "cardones".