Still get most any part I need for 30+ year old farm machinery at the local dealer, red or green.
My gunsmith buddy was able to find a firing pin for a 141 Remington pump for me, gun dates to the 60's. Not sure if that was OEM or reproduction though.
My point was regarding OEM, new production parts for long discontinued models. I realize their are some well established dealerships/service shops that carry large lots of old stock. But those good shops are dindling, too expensive to carry that overhead.
Go to your local car/truck dealership and order a common part for a recent model, see if they have it on a shelf. You'll be surprised what has to be ordered, or worse, back-ordered these days...... I recently needed a commonly replaced sensor on my 04 Silverado, was told it was going to be two to three weeks to get the back ordered part. In other words I would have to wait for the part to be made to receive it. I lucked out, have a good dealership and they dug around for one from another dealership in another state.
Overall you are correct though, stuff is stihl out there for popular equipment if one is persistant and knows where to look.