FWIW, I've had reasonable success with an ancient Xircom (bought by Intel a while ago) RE-100 PCMCIA card in a PCMCIA jacket (the drivers I found said they were for WinCE 2.11 IIRC, but they work anyway).
I also tried a DLink (DE-660 I think) but that didn't work at all.
I suspect that it'll be a problem finding a "straight" PCMCIA NIC these days (as opposed to the newer 32-bit "CardBus" ones which won't work).
I have no idea about CF NICs. It maybe worth asking this q'n in the <a href="http://www.pocketmatrix.com/forums/viewforum.php?f=11">General Pocket PC Discussion</a> forum.