Try getbmwparts as @cy07 mentioned or call FCP EURO and ask for Mike (extension 505):
http://www.fcpeuro.com/BMW-parts/X5/...&m=2133&e=2554. @r33 also might be able to get you the part. You just have to compare prices between those three and decide.
Here's the part number:
51162339010 http://www.realoem.com/bmw/showparts...96&hg=51&fg=16