This query should have been createdin the Chipset forum. This forum is for Intel's Desktop Boards products.
That said, the answer is fairly simple: You want a 1394b card that is in the PCIe x1 form factor. Here is an example of one that should work: https://www.amazon.com/Zopsc-Express-Firewire-1394-1995-1394a-2000/dp/B081JXMDK6.
Hope this helps,