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Difficult one as joysticks can be a bit hit and miss with an iMac. I use a Saitek Pro Flight X55 for X-Plane and although it works perfectly it comes at a high price (about £150).

However, unless things have changed, development of Elite Dangerous for Mac has pretty much ground to a halt...Windows appears to be the way forward for this game.
 
I'm using a SteelSeries 3GC. Works great! Needs to be manually configured for games though, as macOS detects it as a generic USB joystick.
 
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