Welcome to Sailnut.
Last I checked Irwin is no longer in business so you're left with fabricating your own or having someone do it for you.
With high tech lines like Dyneema and others available you might consider using a length of this costly line instead of wire rope.
I'd also be wondering why the old cable broke. Is there a lot of chafe in the run the cable makes on it's way to the center board? Did the cable chafe some part of the hull before parting? Is a block (pulley) missing from the run?
While you are checking out the above you should also check to see if the pivot pin is still in good shape.
You might very well need a few hours with your boat up in a Travel Lift to do this work.
Apparently you can still get the owner's manual for the 34 Citation: http://irwinyachts.com/Parts/Parts_Page.htm