What is the exact model number of the machine? Most Honda mowers start with the verbiage HR21. Could be almost any model. You seem to be missing some information I gather.
I would recommend taking a look at this website to try and find the exact model number for that machine. There is a lot of helpful info there to get you started especially if you're going to be purchasing an older machine.
I have an original 1986 Honda commercial 21 inch machine. I have been using it since the day it was purchased by my father for me to cut grass with (I was 12 years old). In the last 3 years I have replaced every single part on the machine courtesy of that website. You wouldn't be able to tell the mower is almost 30 years old. It looks brand new off the dealership floor.
More importantly, it runs and cuts better than our new commercial model HRC 21 inchers. Just not quite as fast.