Inverted flare fittings are measured different than NPT. OD vs. ID. You won't find a 1/4" inverted flare to AN. Bring your fitting that fits to the hardware store like Blown mentions and match it up and take note of the size.
nice.. I figured something was up since my internet searches came up empty. I will get to the store and figure out what size it is and post back here when I do...