Airbus/Boeing FBW systems use hardened versions of obsolete commodity hardware - the suppliers won't stop making them as long as there's a demand.
IC Part obsolescence is actually a big problem in aviation - our market is too small to justify keeping these components in production when they are decades obsolete in consumer products.
The best option is 'life time buys' - where the vendor stockpiles what they hope is a life time supply of the critical components (IC chips, ASICS, basically any logic devices). Of course, life time buys are not foolproof - not only is it dependent on accurate forecasts of need, but other things go wrong - crates go missing, warehouses burn down, bean counters dispose of what they think is excess inventory, etc.
The second option is to periodically certify hardware packages where they update components and re-certify. This is difficult and expensive - it takes extensive testing and analysis - even subtle changes in things like throughput timing can turn a digital system on it's ear. But it is done (in the last 10 years or so we've had FADEC parts obsolescence updates on both the PW4000/94" and CF6-80C2 FADEC controls - which date back to the mid 1980s).
The third option is just do a clean sheet of paper new device - really expensive and difficult, and often means having to update the associated s/w as well (this is what Pratt did with the PW2000 FADEC, coming out with completely new control - hardware and s/w - around 1995 to replace the original that dated back to about 1980).
But in the end the airplanes keep flying
