Ribbon cable is not available anymore. Alternative solutions are readily available using separate runs of control/sensor wires and RG-6 quad shield coax.
Here is a link to some high quality rotor control wire that would be perfect for actuator motor power and sheilded reed switch sensor:
DX Engineering CW1812OR Heavy-Duty Spec Rotator Cable DXE-CW1812OR
Less expensive control wire solutions such as home security shielded 18g, 3+ sheild wire bundles are sold at Lowes/Home Depot (one pair for read switch sensor and a second if running a polarity servo motor on the feedhorn). Power can be provided via direct burial 12g or 14g low voltage landscape wire.
I would not advise splicing old cables together. Coax cable splices are typical failure points and if the coax has been previously used it may be RG-59 with high signal loss or if older, the dielectric may have been compromised by moisture or age related breakdown. If you do go this route, test before burying.