BMW certainly DOES make a rear shade for the GT
http://www.bmw.de/de/de/owners/acces...er/finder.html
Now, whether you can get the US distributor to get it or install it is another thing. They sell lots of stuff in Europe that they don't sell here. Be interesting to see and price, though. Part alone is 226-euros, which probably includes VAT, so about 19% less here, plus import.