Pita is the fiber of Agave Americana and Sisal is the fiber of Agave Sisalana. Both are used in Spain because both plants have been imported the Ballearic Isles but ONLY agave fibers are used in Spain AFAIK (but I'm no expert). The fibers are nearly identical in pictures with pita being slightly paler.
While sisal rope is rough, that doesn't mean sisal will make a rough sling. I really like my sisal slings, and just made a new one today. The trick is to wet and untwist the cord or rope and then braid the individual fibers, discarding any fibers shorter than about 1/2 meter (or a little over 1.5 feet). It's the ends of short fiber in sisal rope of than make it rough. If you spin it yourself and use longer fibers that won't be a problem. If you're lazy then you can still make a decent sling by braiding the twisted cords together and then singeing the sling to burn off the rough fibers. Tomorrow I'll post a side by side picture of 2 slings made by each method.
I've seen
youtube videos of a man named Diego Camuņas that show how to make traditional, Balearic, 5 strand braided slings made from raw fibers. I've also seen a
tutorial on the Federacion Balear de Tir de Fona website (Balearic Federation of Throwing using a Sling) that shows a traditional, Balearic, 3 strand braided sling made from spun cord. Both are correct.
I find that sisal is kind of slippery, so I've always thought that the leather lining was to improve stone retention before the cast, but it isn't necessary to have a functional sling. None of my sisal split pouch slings have leather on them at all. To be authentically Balearic the sling should have a leather reinforced split pouch and a leather lined finger loop.
Lowes has sisal cord in various size spools. Last time I bought sisal, last spring, it was close to $15 US for 2000 feet. Some ornamental cactus plants are actually agave americana or agave sisalana varieties, so if you know anyone with an ornamental cactus that looks like this:
or
ask them if you can have any leaves that fall off of it.
On my slings, I've found that sisal doesn't fray at all. That means that the cracker won't fray or dissipate.