The only thing I've ever had luck finding in stock at my dealer was coolant.
It takes a bit to learn how to read the parts fische and which drawing has the parts you're looking for in it, but don't be intimidated! Everyone is new to the fische at some point and sometimes all you need to do is stare at it for a while.
Like on MaxBMW (my preference) when you start at your bike model, and start at the Engine section, and go down to the WATERPUMP / OILPUMP - OIL FILTER diagram. There's two drawings, one for pre-1990 and one for post-1990 (just gathered that from reading the part descriptions) and right where the plug should be, there it is #15. There's a note about that part being superseded but I've never been bothered to track down the superseded parts and I just order what's there.
Maybe they ship superseded parts without saying anything? Not sure, but that's what this forum is for, right?