Your user name is apt, as you're going to need such skills to keep that relic going- it's at least 90 years old! Not a later model, a very early one- somewhere 1934-36ish.
You mentioned you are starting a hay business, but one of your first purchases after you get a bit established should be a much better mowing machine- something that will make your hay better quality and you more productive. It's basically the same as advising a rowcrop farmer to get the best planter they can afford. The first step in the process is the most important!
As to parts, the wear items are pretty universal- at least among Deere models- so quite readily available. The pitman is missing (maybe you have it) and maybe not available from Deere anymore, but looks to be findable on-line. The parts at each end are all the same on Deere pitman models; only the wooden stick is different, so possibly a different model mower could donate some non-wear bits.
Your slip clutch looks pretty decent. If you do want/need to replace it, it's part number Z699H. That part was used on a lot of different machines, so should be available still from Deere. Online parts catalog is
here.
ETA: And don't take advice from
anyone who calls a sprocket a "gear"...