Doors and Windows - small door hole in steel door

my bedroom door in my apartment has a small door hole. it's about an inch in diameter, so it's not standard at all. i can drill a 2 1/8" hole to fit a standard door knob, but the problem is that it's an apartment and i can't just do what i wish to the door. so, i'd like to know where i can find a door knob assembly with a chassis that is that size. the existing one has no visible screws that hold together the assembly. the knobs have a spiraled shaft that holds a collar (right after the rose plate) that you can twist/untwist to loosen the assembly so you can get the knobs out. thanks! sorry if this is confusing.

A locksmith should be able to help you. If the assembly is non-standard, the locksmith can order a replacement for you.