Announced at WWDC, and the only way to get Firewire peripherals working with the new Retina Display MacBook Pros and MacBook Airs (besides a Thunderbolt Display), the new Thunderbolt to Firewire cable is now available at the Apple Store online. (Thanks, SchulMarm!)
The adapter ships in one to three business days and is $29.
(Update: the page appears to be off and on)
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