I went with this stuff here for gas just for the convenience of getting it along with all the fittings I needed for a much lower price than midwest supplies.
NORTHERN BREWER: Tubing
The description makes it sound like it should work for gas.
"5/16" Beverage Tubing. Large-diameter tubing is typically found in commercial installations. This tubing fits nicely over the gas-in sides of our commercial beer taps. Sold per foot."
I'm assuming it's ok for gas because of the thick wall.