I have indeed checked those, but from my initial searches it looked like they tend to max out at 8mm. I only found one in 8.5mm but it was in the UK and not cheap. I might check again.You could always check automotive engine parts lists for engine valve stems that have 8.5 to 9 mm shanks. The oil seals have the job of stopping oil being sucked into the combustion chamber during the piston's downstroke on the fuel/air intake with the valves open and preventing the engine burning oil which would eventually carbon up the valve heads and seats. Truck engines as well as cars, or even boat engines, they all have oil seals on their valve stems.
Dima said they used to use them in the old days before he made his own seals.