Where can I find unusual L-shaped brackets?
You could get a length of 1" x 1" x 1/8" angle steel, and manufacture your own.

 

Start by using a chop saw to cut the angle steel into pieces as wide as you need.



Next cut one side of the L to 3/16". A jig will help you cut the pieces quickly and accurately.

Use another jig to help you drill the holes.  A drill press with a carbide-tipped or cobalt drill bit will be useful for this.



Finally, paint the brackets to the desired color using a quality spray paint designed for metal.