There were other Dutch aviation magazines, but my understanding is they merged over the years to be part of "Scramble." I think "Scramble" is now only available electronically. I subscribed to it for a couple years, but it was too Dutch-centic for me.Sounds like you're more clued in than me but I would guess other countries have similar numbers of spotters, enthusiasts and magazines. For example, according to a database of worldwide aviation magazines the Dutch have 3 monthly news-stand magazines, while France has 9 and the UK has 8, plus one weekly. Per capita it's pretty even.
Who are the other "most airminded countries"? Would be interesting to see if they have similarly large numbers of UFO reports.
I can only talk about those I've personally interacted with to any degree. The Dutch, UK ("Air Britian" of which I'm a longtime member), and Japan (can't remember their national group, it was in Japanese.) I know some of the Eastern European nations have similar reputations, but I never dealt with them since it would have been a hassle at work.