I might have to differ on the opinion that Isekis are one of the most difficult to find parts for, in my experience anyway. I don't know about tractor castings ( I haven't needed any and I don't think these are easy parts to find for Yanmar or any other grey tractor from what I've read in this forum), but for the Isekis with Isuzu diesels, the motor parts are very easy to get stateside from diesel supply and repair companies. That's because these Isuzu motors are used in other industrial applications, and the cost of these parts are very reasonable with delivery typically in a week's time. Yanmars are considered to be the easiest grey to find parts for. But like Iseki, you must get your new tractor parts from Japan, but that also includes the motor parts for Yanmars. That is unless you can play games with a JD dealer and convince them that you have a US market Yanmar....and you know the crossover for the part numbers. And even then you might not get lucky. Just my experience.
Bill in CO