What you have is probably the earliest production monohull by Rod MacAlpine-Downie. (one of the greatest sailboat designers ever in my opinion - way ahead of his time). So at least you have a boat that was designed to sail rather than just as a floating object to sit on.
That being said, you need to decide how much time and effort, (and $) you want to put into it, and should you wish to restore it, how close you want to make it to the original. I seriously doubt that the orginal manufacturers drawings still exist. The drawing that is displayed on this site, is the only one I've ever seen anywhere. although you can probably find a brochure on Ebay.
The builder, Starcraft still exists, but they haven't made sailingboats for nearly 40 years.
You will NOT find any parts "off the shelf". If the hull is in decent condition, you should just try to find a left over rig and sails of the same approximate size. (this, in itself, won't be that easy). If you are really lucky, you may be able to find a wrecked one somewhere.
There are companies that will make a new mast for you, and you could buy new sails, but this would be quite expensive. ($2500 at least)
If you still wish to proceed, post some pictures of the boat with as much detail as possible, especially showing the where the bottom of the mast attaches to the boat.
In the mean time, I'll keep my eyes open and see what may be around, If something pops up, I'll let you know.
Best of Luck.