I am building the circuit on figure 33 of the op77 data sheet

I am having trouble picking the correct part for the JFET at D2. The JFET listed in the datasheet is not available anymore. What JFET would be good for the diode connection in this circuit?

 

Not sure why they use a JFET there instead of a diode but just about any N-channel JFET should work.

 

I recognize that circuit from here http://sound.westhost.com/appnotes/an001.htm and here http://www.analog.com/static/importe...45851AB109.pdf
The FET is connected as an diode, and FETs have much lower leakage current than a PN junction. And that may be the reason for using a FET in this case. As opamps may often have very low input bias current.
It looks like the FET you need is stocked by Mouser But I guess any simelar N-Channel JFET can be used
http://www2.mouser.com/ProductDetail/Central-Semiconductor/2N4393/?qs=Ypxpq5eNvNUGYaNfe7VA0Q==