There are few company making aftermarket wheels for X5. The big brands are listed by PNG. Others include

Breyton
BBS they make OE wheels for BMW
CEC for Antera and CEC Alpine
DPE
Velocity motoring
Radenergie
BRS
MIRO by Jlevi
Falken
Monet
Beyern
Savini
Kinesis
MST
Vorsteiner
I have seen Overfinch on X5 too
OZ at Tirerack
Moda at Tirerack
Rays wheels at Tirerack
TSW

Ebay Stores selling replicas and others
Lakeshore Wheel And Tire
Euro Tech
Blustar
Wheels and caps
Euro wheels
Get Your Wheels
OE Wheels
http://factoryreproductions.com/bmwx5.htm