You could go to your local BMW dealership’s parts department and have them order you one...or go to one of the online part databases and pull up the diagram to get the 11 digit BMW part number and look for it online (used in the color you need) or new & primed (to be painted later). You could then look locally for someone to paint match it...or go online and buy a can of spray paint based on the color code on your VIN sticker...and you could spray paint it yourself.
You need #5 in the diagram below:
I purchased a can of space gray paint from either an eBay or Amazon.com vendor that was based on my exterior color code A52 (space gray) and it was a perfect match. You could do the same for your exterior color...just make sure you use the correct exterior color code...again found on your VIN sticker in the lower right corner. Once you have the correct color code...just type
BMW “XXX” spray paint (where x=the actual color code) into an eBay or Amazon.com search box.
You can see the exterior color code in the pic below...look for A52/7 in the lower right corner...
A52 is the exterior color final coat and the
7 is the base coat color in this example