It has a Kawasaki fd590v-as00 engine what will fit

Hi,
First you have a rare machine with a distinctive hood, and an excepional engine. Is the engine locked or run low on oil? Could it be one of those with the bad camshafts?
At any rate one site to check would be:
John Deere 320 Category
And another site will give you a comparison of prices:
21-29 Horsepower Kawasaki Engines On Sale At Tulsa Engine Warehouse
And you can also price it through Deere. It probably is comparable to the second site, but will be built as a completely Deere drop-in replacement. Sometimes Deere will have stock they need to liquidate and will have exceptional prices to do it.
All in all, That is an exceptional model and well worth the expense if it has had a well-maintained life.
Peace,
Clarke