It’s quite likely that some internal tap rubbers may no longer be available but it doesn’t mean your tap is toast. If you have a good mate or friendly dealer try out seals from other makes. It’s more than viable to run a Honda rubber in a Yamaha tap for example. If the rubber or the holes are too small then fettle them. The OD can be carefully trimmed down with a hobby knife whist the holes can be opened with a sharpened hollow tube of the correct diameter. And if there isn’t a readily available tap rubber to hand you can always make one from some viton rubber sheet; ebay lists the base material in a variety of thicknesses for just a few quid.