Serial leads can be obtained from ??? the cost is around $25,
in the uk try http://www.2k1.co.uk/ the cost is around £25, the service is rapid and efficient.
Some useful part numbers:
Don't forget, for the old "slab" style boards you need a different lead than the newer "FPGA" style boards .. the older boards use a RCM2300 series Rabbit, the newer ones use a RCM3300 device ... different header dimensions.