Pearstone 6-pin FireWire-400 to 9-pin FireWire-800 Adapter
OWC Mercury Elite Pro FireWire 800 & USB... at MacSales.com
Rocstor LANCER LX Ruggedized USB 3.0/FireWire 800 Mobile Drives, (DISCONTINUED)
Amazon.com: 4 Pieces Firewire IEEE 1394 6 Pin USB Adapter Female F to USB M Male Cable Converter Firewire 6 Pin to Male USB 2.0 Adapter for Printer, Digital Camera, Scanner, Hard Disk : Electronics
Apple Thunderbolt to FireWire Adapter Thunderbolt Male To FireWire 800 Female, MD464LL/A | Full Compass Systems
Connecting Firewire 800 drive to USB C | MacRumors Forums