This sounds easy, but in my experience it was pretty hard to find a used Kubota with low hours that wasn't just 10% or so less than a new one. I had finally resolved to just buy a new one and had about pulled the trigger on a brand new 50hp Kubota when I found a 10 year old 45hp Kubota with 930 hours for about $10,000 less. (I got it for $12,000).

To find one you need to check online, check your local paper, and it actually took me almost a year before I found the one I bought.

Here's a website that has a lot of used equipment - http://www.tractorhouse.com/