Please not from a florist - as they will likely be sprayed with pesticides.
I'd also suggest growing them if you have a balcony, and otherwise picking.
What also works well are herbs, just potted herbs (you can also put them in the enclosure with the pot so they are as fresh as possible). For that, either grow them from seeds (outside of the enclosure, and only putting them in when large enough) or getting organic potted herbs from the veggie section in a supermarket.
My dragon is used to eat from live plants, as this also gives him access to fresh leafy greens when I'm away for a day or two.
The zucchini flowers are often available at farmer's markets (these are the male flowers they remove). But if you have a balcony and are into giving it a try: Zucchini grows well in pots.
(I have the herbs, sadly can't grow the flowers as the climate is too harsh here, but from my gardening experience in more moderate climates, all those grow well.)