bath tub drain

I want to replace a tub drain. It 2'' in diam. with fine threads . It's about 30 yr. old with brass finish made by Kohler. Where can I find something to replace it with?

The 2" diam. tub drain is unique to Kohler. You can possibly find a replacement, and if not, aftermarket companies make bushings to adapt to it. You will not find these at a local hardware store. You will need to go to a large plumbing supply house.