I couldn't find a pre-made solution I liked, so I made my own:

Materials:

- 1/4" thick piece of lexan
- 1/2" x 1/2" x 3" piece of Delrin
- 4 cap screws
- 1 rail mount - originally was a bipod adapter

The deflector attaches to the handguard. Installs in 2.5 seconds, removes in 2.5 seconds....

You can see in the last picture how effective it is...