I've never actually seen the complete setup for a sickle bar mower on a Cub Cadet. However, I do know they were made by Haban, and I believe they utilized the front PTO and two pulleys on the mule drive assembly to get the belt run down to the sickle mower part where it mounts in the mid section of the tractor. Those parts are standard Cub Cadet and readily available.
Haban still makes some equipment/attachments for various machines, and I would think if you have part numbers you could find what you need on the internet. Having said that, I have never looked for anything for Haban equipment. However, I would bet, based on other equipment of their's that I have worked on, it is all standard dimension stuff that could be purchased from McMaster Carr or maybe even NAPA.