I don't believe Lunch with a Disney Artist is available since the Animation unit is closed down. I was lucky enough to do this lunch in October with my daughter.
The Brown Derby does have Lunch and Dinner with an Imagineer. The lunch is about $60, and the dinner somewhere in the $90's. When I booked our lunch I went through Disney Dining, and the CM found it under "shows". I could only book the experience 30 days out.
The food and the experience were great--we're thinking about booking with an imagineer on a future trip.