I think both them and BMW have all the tools to make any part they used on production models. Not sure exactly how far back either catalog goes, but from what I've heard it is total for even 60s & 70s and maybe 50s models. Of course the way out of date stuff will cost but they could make something for you if your really want it.
Dealing with BMW is hilarious because you will end up speaking to some guy either looks about 14 or like God's older brother, and he will say either "Ja so this part, I will show you how you take the beer can and you cut a piece like this, oder so, and it will fit over this and it is ready, ja? Ausgezeichnett, ja?" or he will say "Ja so this part, it is a special order from Munich and it will be four thousand euros but we will have it tomorrow" and the customer being German will just pay it and pick the car up after work tomorrow, and that's it, end of the story, done.
Or the customer will be Austrian and there is nothing for it but assassinating archdukes and bloody warfare over a 1.50EUR gasket.
BMW’s online catalogue indeed reaches back to the 60s: https://www.bmwgroup-classic.com/en/services/spare-parts/bmw...