Do not use FireWire to USB adapters. These will damage the board.
The original Apple FireWire to Thunderbolt converters work well. Please contact me for a quote if you can't get a calculation. This item is in the category "Computers/Tablets & Networking\Printers, Scanners & Supplies\Scanners". The seller is "scannersandparts" and is located in this country: GB. This item can be shipped worldwide.