It's 5/16X14 but the joint wall is thick, so some shaft tenons will be too thick to fit.
The joint looks like it's 7/8" outside diameter X 1/2 " inside diameter. This is a standard size but you should check it closely. Once you confirm the measurement, you can order a shaft based on that info. I personally would still have one fitted - to be sure the shaft aligns properly with the handle.
Since you want a leather wrap too, the three guys I would suggest is Scot Sherbine, Ryan at Meullers, or Mike Webb. They all get the work out quickly and do a nice job at fair prices. You can expect to pay around $250 for a fitted shaft (OB or Predator) and $100 for a leather wrap - give or take a little on these prices.
Chris