To keep from getting nickle-and-dimed on my automotive plumbing projects, I've been using Discounthydraulichose.com for about the last ten years
Most of my projects use various sizes of AN fittings, and the steel JIC fittings save a lot of money. A quick check of their website shows they sell brass air fittings too.
FWIW, the truck in my avatar has an airbag suspension. I tried the push-on connectors and couldn't get the leaks under control, so I took them out and plumbed it with -4 AN and hard line. The combination of the aluminum 5052 hard-line and the steel JIC fittings make a pretty reliable seal. With the push on connectors the truck would only hold air for a couple of days - with the hard-line it'll hold air for a couple of weeks without a recharge from the compressor.