Varithyxx Frontier Mountains
 

I have done the FM cycle many times and have not seen Varithyxx spawn once ever since Kunark opened. He should be on the sarnak spawn table. The sarnak cycle seems bugged and inconsistent.
Here's a fairly old link that outlines the cycle as it was on live.

http://www.paullynch.org/eqblog/?p=44

You may have had bad luck with the RNG.

I've done the cycle maybe 3-4 times for several hours each and seen Varithx spawn once, no sleeves :(

He seems to be very rare or we're just unlucky.