Just from Googling, one broker claims to have stock on a 3SK166,
3SK166-1, and 3SK166A. I have never dealt with this broker before.Brokers like this one buy up inventories of old parts from other suppliers, and/or send out random parts with false part numbers on them. Sometimes you will get the genuine part at a bargain price, and sometimes you will get a part that does not work at all.
I have cross-posted this reply to sci.electronics.design, which is much more active than sci.electronics.components . It also has people smarter than I am who might be able to suggest a replacement. :)
What claims to be the Sony datasheet is available at:
Some of the interesting parameters seem to be: Vds 8 V, Vgs -6 V, Id 80 mA, Pd 150 mW, gain about 20 dB. The datasheet gives S parameters and noise figures for a range of 200 to 2,000 MHz. The package is a Sony M-254; it doesn't list an EIA or JEDEC package code.
Standard disclaimers apply: I don't get money or other consideration from any companies mentioned.
Matt Roberds