I grew a bunch from seed from King's - note that when grown from seed you tend to get a lot of really spiky artichokes. (Painfully spiky as I keep finding out :)
You'll get a better quality artichoke if you take suckers from a plant that produces good heads already - I think the plants sold at garden centres are usually from suckers rather than seedlings.
Not sure if this is any use to you - but I have lots of seed heads from last year's artichokes. Only trouble is, as we don't eat them, I am not sure what sort they are! But they are definitely artichokes! Happy to send you a head off the plants - we've got heaps!
Mitre 10 sell them in their herb section, they are very easy to grow from seed as well, King seeds sell them. If you lived closer I would give you some!
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You'll get a better quality artichoke if you take suckers from a plant that produces good heads already - I think the plants sold at garden centres are usually from suckers rather than seedlings.