Is this stuff any good? It doesn't appear to be manufactured anymore.

My Arsenal 104 shoots really well with it.

Any idea why they don't appear to be making it anymore?

Most of the 5.54 is going to military contracts. The folks that make the stuff are geared to that and the commercial market is suffering.
Nothing magical or mysterious, just supply and demand.

Reason #12349 y'all make me a happy customer.

FMJ 5.45x39 Silver Bear is all that is imported these days...

The destruction of the Lugansk Cartridge Works killed like %30 of the total 5.45 production capacity for the round and something like %45 of the new commercial ammo production. Tons of wolf/barnaul product came from there and was rebranded under various head stamps.

Combine that with the loss of 7n6 surplus and that most new Russian ammo is by nature AP and un-importable, the 5.45 could be in trouble.

The tooling from LCW, which provided a significant portion of ammo producing equipment during soviet times, was smuggled back into Russia and supposedly went to an existing factory.
The word is they are setting up new production lines with it so maybe the volume will increase. However that ammo could be subject to sanctions potentially. There are pending court cases over the incident.  

True and not true. the fact remains that they produced upwards of 30% of global 5.45 supplies since soviet times. LCW was who invented the 7n6 cartridge as they figured out how swage the steel core and make it accurate.  Also prior to 2013 they operated under a number of different brandings "LCW" is a new name for a very old soviet factory and tooling center. Most of that ammo that surplused out years back and was selling for 11cents a round was from Ukraine and lots of it was made at LCW although youd never be able to tell. The LCW case mark and brand is recent. They used a soviet factory number as well as cyrillic letters on their stamps prior. They also often stamped ammo as wolf but was boxed in Russia and said made in Russia. The also  made silver bear golden bear hotshot and tula branded ammo there over the years. Unless you where a forensic tech you would not be able to tell where the ammo came from. A fact that always seemed shady but was a carryover from soviet cross border industrial actions and the fact that some Russians held sway in the company. Ukraine also had some type of ammo export ban for years, hence using Russia as a middle man. They also provided components and tooling to Russia in great quantity. Its a five minute drive from the factory into Russia. That was normal business there prior to the war.