PCIe Ethernet NIC Compatibility

All, we’re in the process of building up some unique support for clustering on top of the HiFive Unmatched platform. Rather than using the PCIe slot for a graphics card, we would like to install an additional ethernet card. I’ve sourced the actual Ethernet phy part #'s from the various RISC-V open schematics (in order to check driver compatibility). However, I can’t seem to find any externally available PCIe boards with the same part numbers. Does anyone have any experience installing/using external Ethernet NIC cards that are known to work with the Unmatched platform? There are plenty of boards with drivers in the existing Linux kernel (we plan to use the Ubuntu 21.04 loads), but if someone else has tested external boards it may save us some time in debugging one.