Your local BMW dealership's parts dept should have it (order it). Or...if you go back to that diagram...scroll down to item #6 and get the 11 digit BMW part nbr...then type BMW xx xx x xxx xxx" (where x=the part nbrs you found) into a google search box (or BING) and you should see some other vendors that sell that part.
More than likely you'll need to purchase it from another BMW dealership because they can order it specifically by the "code" that you gave. You may be able to find an aftermarket/online vendor that may be able to get it for you...but more than likely, they'll have to order it from BMW, too since the "key" has a specific code to match the bolts of the rack set you purchased.
Good luck.
EDIT: For example, I just looked up the 11 digit BMW part nbr for item #6 & ran the part nbr on my local BMW dealer's website and they have its MSRP as $11.73 & they sell it online for
$8.80 (again, the "H0" code is required when ordering):
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