Spectral, when last I spoke with them would not touch something if anyone else had been in it.Wow, that's really lame support. If I was in their position, I'd WANT it back so I could be sure that it was working the way it was supposed to. Of course if somebody had made a mess inside I'd charge accordingly . . .
But for your part. IIRC this is the same as a 2N5566, which is a dual matched JFET. If you google it into the ground, you can probably find one. If not, you might contact Erno Borbely, he's passionate about using matched-JFETs in his own designs, and may have some ideas for substitutes. Also there's a company called Linear Systems that makes matched JFETs . . . I've tested some of their samples and they seemed to work well.
If your technician is making substitutions, make sure that he/she is properly equipped to check for parasitic oscillations at a wide range of frequencies and power levels. Checking for IMD isn't a bad idea, either. I'm assuming that Spectral is using this part in an input differential amplifier, so substitutions/problems here can definitely affect performance.