CS3s are on my 19" 309s too so I assume they are fitted to quite a few new X3s, and despite this, BMW can't source them, and yet they charge for "insurance". Hmmmm.
Not sure what the smallprint says but can't you push for both tyres being replaced on the claim, or accidentally drive over another nail?!
Let us know how you get on - good luck
BMW X3 (F25) xDrive20d SE . . titanium silver . . titanium front grille . . 309s . . xline . . xenons . . black leather . . alu trim . . professional multimedia package . . dynamic package . . climate package . . electric seats . . folding mirrors . . servotronic steering . . DAB radio . . business speakers . . sun protection glass . . split rear seats . .