The Mindscape appears to have a pistol grip, which doesn't fit the description the way I read it. I remember seeing an Epyx 500XJ back in the day, that seems to match the description better. I thought I remembered it with two buttons when I read this post but the picture just reminded me of the blank space where the other fire button should be! Maybe there is a two-button version of this in existence. It's a shame more joysticks weren't produced with two buttons (as in two different buttons, not just wired together on the same pin!), and games written to use them both.
Personally, I use Sega Megadrive pads. Good on Sega for using a pre-existing standard! Although pins 7 and 9 are unfortunately the wrong way round for the Amiga to access buttons A and Start. An adapter would be easy though.