There's a good amount of cars running n2 flares in the US, so check what sizes they are using, should be easier to get the specs from at least and enough cars to make a call on what size you would want.
Chris Lee, Miataturbo guys, the brits (madabout), samulis.
And this thread reminds me of how much I want the GHO front + n2 flares... droooooooooooool