Disclaimer: basically no MHz experience.
I would start by looking what modern computers use for high datarate connectors:
These should be very easy to get. Also consider the smaller:
EDIT: Cardedge is probably fine, provided you do things like ensure each transmission line is a similar length.. I
presume stub/reflection behaviours won't be a problem (when no card is connected) as wavelength of 100Mhz = speed of light / (100 * 10^6) ~= 3 meters , but I'm probably using the wrong logic here.