For old cables, you are often better off trying ebay,Analogic charged me £80 for a modem for the mac, I needed internet access & could'nt find any modems on ebay & wasn't sure about the cable connection.
You would pick up the same off ebay for £30 max.
do a little diagram of the plugs/sockets, that you need cables for.
Try Belkin.co.uk , Macwharehouse.co.uk OWC.com
It can be a real pain in the backside but be patient & it will probably appear on ebay.
shaktiman
Quadra 840av, prettymuchmaxedout8xcd drive,3 monitors 15" & 14" & 14" os 8.1
, 12 meg ram, 500 meg hard drive
Performa400(asleepintheattick)