The plastic disks can be drifted off if you stand the shaft over a washer sitting on the vice just wider than the rod diameter. Most likely you will find that the shaft is straight knurled in each roller position but it is still a very useful, (easily machinable) grade of steel.
Rubber wheels are glued or bonded and not easy to remove but you could try VERY tightly compressing the bush across its diameter in the vice and sliding a stanley on the shaft and slice off a lump to see what lies beneath.
Modern domestic grade printers contain a very limited amount of reusable material and nowadays don’t make rich pickings. Older laser printers, especially early HP models are an engineering treasure trove with substantial construction and lots of steel and brass gears.
I have never found any stainless or difficult to machine shaft in the ten or twenty printers I have cannibalised.
Ian P