Well, it's hard to tell what you need from the problem statement so far. Is lack of compression your only problem? What is your compression cylinder to cylinder?? Is your oil pressure OK? Does it run hot?
Parts are readily available somewhere in the U.S. You need a good relationship with a dealer who can search parts for you and you probably need to start developing a contact here:
http://www.kubotaengine.com/index.html
I'm just finishing up what I call an "in frame" rebuild to resolve the same lack of compression problem. In my case, I was able to get by with rod bearings, rings, a head rebuild and a few gaskets. I'm all in at about $550 including the cost of the machine work ---
So, you can do it. First, you need to figure out "how bad is bad".