Hi Petri,
If your E23 was built earlier than 9/1985 you got coarse splines, you can fit wheels from E12, E21 (1979->secound series), and early E24 series (first series ->1982).
If it's built after 9/1985, you got the fine splines and unfortunatly, there's nothing that I'm aware of would fit ... "maybe" those from E24 secound generation???
Regards,
45er