I think having a local dealer is pretty darn important. I'm a homeowner that cuts a only a few acres once a week and I know that with any machine, s#%*! happens. At times I've ordered parts online and fixed what I could myself, but there is nothing like running 10 minutes down the road to get a part right when you need it. But parts are one thing, service is another. Unless you are a mechanic, you will occasionally need to haul it in and 5 hours away would be some serious butt pain.
You might ask the Exmark dealer if they would service a gravely.