I know that I am fortunate in that I have two BMW dealers close by, but I have never understood the “key availability/buy a blank on eBay” deal. I walk across the road from my work into BMW Ducati Husqvarna Motorcycles of Atlanta http://www.bmwmcoa.com/
and they have folding and non-folding blanks in stock. Cutting takes a moment or two. From memory, a cut folding key is around $10 and a cut flat key a good bit less. I have to believe that any BMW dealer has the same setup. I think there might be a trick if you want someone to cut to the key code rather than than a pattern.