I am afraid there are no single parts available from the dealer.
Only the housing center item # 3 complete
http://bmwfans.info/parts/catalog/E3..._conditioning/
Part number: 64 11 1 374 325 $ 236.50
options: get the upper part from a used one
or
make a aluminium bracket or from plastic, where you have the possibilities.
As a used one will probably also be brittle, I would try to make the brackets DIY.
Make as many pics as possible, and send them to me, to the link on my website, to Hairywithit, he will include that on the site. Will be good for future help.
And a short write up would also be good.
And when you have the parts made, new busines for you ;-)
many people will need them.