In the states, here, you can usually find a used shaft. Or you can have one made at a driveshaft shop.
To find a used one I'd start with Classic Mustang Parts of Oklahoma 405-631-1400m
www.ilovemymustang.com.
I've never used them, but they are always in Hemmings. Now shipping it to Chile without damaging it, well that's another story.
FYI, the last driveshaft I had made. The shop just wanted the measurement from the differential yoke to the outside edge of the rear transmission seal, measured with the car on the ground at ride height. I also told them what the spline count was on the front yoke and what u-joint was on the rear. Two days later I had a brand new shaft.
Hope this helps.