McMaster Carr has quenching oil, and a 5 gallon pail is $80 plus shipping. They have two viscosities, but do not list the precise viscosity, just quench times. One is 11 seconds and the other is 28 seconds, You can call them and ask for the particulars. The 11 seconds is close to Park 50.
https://www.mcmaster.com/#quenching-oil/=16wupmc