Best source for Kohler Oil Filters for my GT5000?

I get mine from Napa (crosses to a Fram PH7575)

Price is around $2.50/filter if you buy a dozen

Absolutely. The Magnusson-Moss Warranty Improvement Act states that if a manufacturer requires a specific brand consumable to be used (Oil filter, spark plugs, etc) in order for the warranty to be valid, the point of service (repair shop or mfg) must provide the product free of charge. The product must meet the manufacturers specifications in order to qualify.

I learned about this extensively via my 5 years working for Autolite in the early 1990's.

It does apply to lawn tractors, automobiles, and even clothes dryers, etc.

Believe me when I tell you that Autolite, Fram and Bendix as well as other manufacturers design to OE specs. They do not want the liability of causing engine damage do to one of their cross reference charts. That is why they have the cross reference and application sections of their catalogs.

If it is in the catalog, feel confident in the spec have been met.