Yes, the release cables (and the sync cables) are special items for the Sinar shutters. It happens just a bit too often that these shutters are for sale without these items and sourcing them can be a very expensive experience. I.e. if you are buying one, beware of those without the dedicated release cable and sync cable. (The "stop down cable", which closes the shutter and sets the aperture on Sinar DB lenses is an optional item, which isn't necessary, but nice when shooting a lot as it saves a bit of work and cuts some seconds of the shooting time for each shot. I.e. once you've decided on your shutter time and working aperture, set both values on the shutter (aperture and shutter still wide open), push in your film cassette (and the shutter closes), take out the darkslide and shoot (and the aperture closes to the pre-set value).)

I've seen some descriptions on how to make/modify an ordinary release cable, which may work, but the original item seems a lot better.
But don't let this turn you off the idea of the Sinar/Copal shutter. It's a very sturdy shutter, which will last for a very long time doing heavy duty service. Even though the shutter sounds like a car crashing through the wall of your studio with the vibrations to go with it, these vibrations comes as the shutter closes so they will not show as a vibrating camera.

//Björn