I remember when this stuff happened, and I didn’t live anywhere near farm country.
See: https://archiveattic.wordpress.com/2008/12/09/fatal-bank-and-farm-shootings/
Also: http://eightiesclub.tripod.com/id395.htm
I'm sure there have been isolated cases. But like school shootings, farm-related violence incidents get wide coverage exactly because they are rare (given the relatively small number of farmers, they pretty much "have" to be rare) in a country of 300,000,000 population.
The media is quite fond of purveying isolated occurrences taken out of statistical context.
Thank you for that links. Now I will know the keywords for more digging.