Never dealt with these guys, and it's too bad they don't have a parts schematic on their site, but Jack's Small Engine seems to carry some stuff for Yazoo-Kees. Might be mostly newer ZTR stuff(?). If you have a part number, you can search using it.
Found Schuuman's Farm Supply that has parts manual downloads for Yazoo YR models. Not sure what model your's is.
The Yazoo-Kees site has user manual page, but states "If you are looking for an older discontinued product, please contact Technical Service by using the email form in the Company section." Might be a way to get the proper manual so you could get parts numbers to cross-reference on other sites, like Jack's.