OK, after a bit of searching I found the .rpm. So I tried...
rpm -i /mnt/cdrom/SRPMS/kernel-pcmcia-cs-3.1.31-13.src.rpm
...and I get
V3 DSA signature: NOKEY, key ID db42a60e
To a Newbie like me this conveys nothing. I've done a google search and found lots similar questions about this - but not one answer