Get a short roll of 10" or 12" wide roll flashing, I have seen it at Lowes less than $10 for a 10 foot roll. The 10" wide will make a 7" visor the 12" will make a 9" visor.
Cut to length adding about 6" on both ends to be safe. Screw it on to a piece of 1x4, drill holes first for the screws, it's easier. Flip over and then fold back so that the flashing is bent over the board. The board will be your mount to the blind, the flashing can be bent to a "visor" shape.
Aluminum bends easier, but galvanized is stiffer and will hold it's shape better. The wind can and eventually will play hell with these. I would also paint it before I put it on. Be sure and wear gloves, this will be sharp.