All I can think of is get a Leica 21-35mm and a mount conversion kit.

+
The lens is supposed to be one of the best, if not the absolute best, of its kind.

-
$$$$$$.
You have a completely manual diaphragm.
You need to change the mount (or have it changed - reversible if you want to resell later).
21mm might not be "wider than 21mm".... But then some "20mm" FLs might actually be longer (many manufacturers declare optimistic figures).