Wow, you aren't kidding. I just checked Onsemi and Vishay and neither makes lateral mosfets anymore. I'm surprised because many audio amplifiers still have a linear output stage, are those just always BJTs now?
Most of the linear amps these days are integrated devices that need a few supporting components and you feed a line level audio signal. Though you can still get decently sized BJT's and you can build your own amps.