Part numbers are listed in the Yamaha service manual for each instrument. In the USA, service manuals may be purchased from Yamaha 24x7, their on-line portal for parts.
The main issue is gathering together service manuals for all of the relevant keyboards! The service manuals are not especially cheap even though Yamaha distribute them as PDF files. If someone undertakes this task, please note that the 88 key "piano action" models have a separate manual from the 61/76 models with the FSX key bed.
Do you want to compare part numbers for the individual keys or the entire keyboard assembly? There are separate numbers for all.
Hope this helps -- pj (a service manual diver)
Music technology blog: http://sandsoftwaresound.net/