This is another p/n that's been used in the CA:
IXTY08N50D2
per the link I previously posted. It is also not presently available, but it's specs are
Transistor Polarity: N-Channel
Number of Channels: 1 Channel
Vds - Drain-Source Breakdown Voltage: 500 V
Id - Continuous Drain Current: 800 mA
Rds On - Drain-Source Resistance: 4.6 Ohms
Vgs - Gate-Source Voltage: - 20 V, + 20 V
Vgs th - Gate-Source Threshold Voltage: 4.5 V
Minimum Operating Temperature: - 55 C
Maximum Operating Temperature: + 150 C
Pd - Power Dissipation: 60 W
Channel Mode: Depletion
Specs on your existing one
Transistor Polarity: N-Channel
Number of Channels: 1 Channel
Vds - Drain-Source Breakdown Voltage: 500 V
Id - Continuous Drain Current: 350 mA
Rds On - Drain-Source Resistance: 10 Ohms
Vgs - Gate-Source Voltage: - 20 V, + 20 V
Vgs th - Gate-Source Threshold Voltage: 3.5 V
Minimum Operating Temperature: - 55 C
Maximum Operating Temperature: + 150 C
Pd - Power Dissipation: 2.5 W
Channel Mode: Depletion
I would presume that of those specs, and the ones of the one already on your CA, the ones that match closely should probably also match closely in the new part you use, and the rest may not matter, other than being "at least as good as" the worst-case version of them. I bolded the things that are the same, and underlined the "worst case" (minimum requirement of the two) of the specs that both have available. If the part you can get has better specs (higher current, higher watts, lower ohms, etc) then all the better.
But this is the specs for the part you suggest, and some don't match or aren't good enough, particularly that it says it is an Enhancement mode FET rather than Depletion mode (according to JustinLE's post in that thread, it must be a Depletion mode). I italicized the problematic specs:
Transistor Polarity: N-Channel
Number of Channels: 1 Channel
Vds - Drain-Source Breakdown Voltage: 100 V
Id - Continuous Drain Current: 5.8 A
Rds On - Drain-Source Resistance: 350 mOhms
Vgs - Gate-Source Voltage: - 20 V, + 20 V
Minimum Operating Temperature: - 55 C
Maximum Operating Temperature: + 150 C
Pd - Power Dissipation: 2.5 W
Channel Mode: Enhancement
I am not sure what would be a good choice for replacement; I have at least one (probably two) CA3's here that need this repair myself, but haven't gotten around to looking into it. Too many projects. :/
The post by JustinLE in that thread I linked before does mention how you might get a regular FET to work, though I never tried it.