According to most sources on the topic, Oahu only has one coffee estate at the moment.
Waialua Estate Coffee and Chocolate is part of Dole Food Company Hawaii and started in the early 1990s growing Kona Typica, a very valuable varietal.
The farm seems to have spectacular views, as it's located over Oahu's North Shore, surrounded by mountains. From there, you can see Koolau Mountains to the east and the Wai'anae Mountains to the west.
Most sources claim that farm tours are available, but under current circumstances, it's always better to contact them directly.