Make your own 12mm wide bias binding with the Clover bias binding maker. 
Cut a strip of fabric. You can find the right with of the strip in the user manual. Insert the strip in the maker, place your iron on the end and pull the maker backwards, following directly with the iron.
You can also make fusable bias binding by adding a strip of Bondaweb.

Available in 12, 18, 25 and 50mm. This version is yellow, the other witdhs have a different color.