I would likely simply use the hardware store, not big on official Honda parts after the way some Honda techs have treated me in the past.
Also depends on exactly what you are calling a sync screw. the ones that plug the holes or the ones you actually adjust on the linkage?
(edit) I see.............. the ones you adjust with..................that'll be a dealer only part there, it is a screw with washer and spring incorporated as one assembly. Or bike scrapyard or ebay. The thread there is ultrafine and not found out in the marketplace.