Have been hunting with this same gun since I was 12 years old. Never heard about Remington stopping this line. Better stock up myself. Oh well. I can still find ammo for it at my local walmart, and most sporting good stores.
I remember reading years ago that this cartridge was made many years ago (1800's late If i remember right) and WAS one of the best deer hunting guns. I would have a hard time believing they would toss it aside for other guns.
But better safe then sorry.... Have about 250 brasses. that should be more then you need for the life of the 336.