I imagine its the same knob that fits an e46 and I bought mine from ecs tuning.
I went with the lighted one looks cool. Also I went with the alacantre shift boot too.
This shows what I did when I did this on my e46 car.
Shifter Mods | Crowz Nest
But it should be same on the X5 I would think. You can cross reference the part numbers to be sure.
I went from this :
to this :
Which looks like this at night :
