Best Buy stores should begin stocking this cable as it is huge in the A/V world. A lot of older video cameras and music equipment rely on Firewire 400/800 to operate and I think Best Buy is missing out on a huge opportunity by not stocking these. On Amazon this cable ranks #97 out of the top 100 best-selling cables.
[Description from Manufacturer]
Easily connect your Thunderbolt-equipped Mac to a FireWire device with the Apple Thunderbolt to FireWire Adapter. Small and compact, it connects to the Thunderbolt port on your Mac computer, giving you a FireWire 800 port that supplies up to 7W for bus-powered peripherals like hard drives and audio devices.