Edit: Just caught that you might not be allowed to use buffs, so my recommendation is not applicable but I thought I would leave it up for anyone curious about this question.
Double Edit: Just took this gaiter for its first long run and its dye is not colorfast! I nearly ruined a nice singlet with the weird sweat drop stains it left
We have had an odd run of weather here lately that has required me to hit the treadmill for some of my longer runs, which has meant running in a mask.
For what it's worth, in a pinch, even the basic disposable masks you get at the grocery store work just fine for running once you get over the initial discomfort. However, I really like
the Cooling Gaiter from Mission, which has been really comfortable.