Just about any PCIe (PCI express) firewire card should work.
Here are just a few:
StarTech 3-Port FireWire 800/400 (1394b/a) PCIe Card Adapter
SIIG 1394 3-port PCI Card Model NN-440012-S8
SIIG FireWire 1394a 2-Port PCIe Card, Model NN-E20012-S2
2-port of 1394b + 1-port of 1394a Firewire Ports PCI-Express Controller Card (SY-PEX30016)
If you are running Windows 8.0 or 8.1 you will need to download the legacy firewire driver