RealOEM.com * BMW E53 X5 3.0i ALTERNATOR PARTS 90A Valeo
This may not be the correct alternator so you should follow the link and back up a page or two to see what the options are. No matter which alternator you have, all of them have Item 2 as the voltage regulator. The regulators may or may not be the same, but you can do a little bit of research to figure this out. The link is also the parts for the I6 engine, so you will need to change the vehicle information, then go back to the engine electrics page to figure out the alternator that you have, and the VR that you need.
Once you find the VR that you need, then you can shop for best price from online sources, or the auto parts store down the street from your house.