What's the best source for a 92FS replacement barrel that's in-stock?  Threaded preferred, but not required.  Is factory beretta the way to go, or is there a reliable aftermarket manufacturer?  It's probably a 1990s vintage model, if that matters.

Usually Beretta is reliable because it drops right in. I don’t have experience with other manufacturers but I did look at Jarvis custom, Bar-sto and Silencerco.

Check Beretta store I just got a inox threaded full size w/coupon code was about $150. Not bad for plandemic prices. Also came with new locking block installed.

@WI_Bill
For all your Beretta needs...
https://www.midwestgunworks.com/beretta-92/parts.html
https://www.midwestgunworks.com/beretta-m9/parts.html
Click on the red number to take you to their inventory and pricing.  

or

https://www.gunpartscorp.com/gun-manufacturer/beretta/92/parts-list-92

or

https://www.apexgunparts.com/handguns/beretta-pistols/m9-m9a1-beretta.html

OP also I'm not sure if you're picky, but Beretta sells the Italian made and American made barrel.  The Italian model will have a serial number engraved on it and says made in Italy, while the American made barrel has nothing engraved on it.  Beretta uses the exact same stock photo on their website for the American and Italian made barrels, so you can't tell any difference...until it arrives at your home.  But in real life you can tell the two apart very easily.  The Italian barrel also is $30-40 cheaper than an American made barrel.