If you don't have the 2SK2539 you can build the circuit with any Jfet. The biasing may require some adjustment. I substituted J112s and it still function but at a lower gain.
Look at the first set of curves on the last post. You would need a 3.3K Ohm or 4.7K Ohm resistor with that Jfet to get 1 ma. It would function if built using the 1K Ohm but would have a very high current drain on the battery.