I like to consider the voxel-based, sci-fi flying sim Rescue on Fractalus! by Lucasfilm as the predecessor to X-Wing, but you can safely ignore me. Besides, no matter how you look at it, the game was an innovation in both design and tech, and one of the first properly scary (rarely, but effectively) 8-bit offerings.
To own a boxed copy of the thing, you could bid on this Rescue on Fractalus! eBay auction. It's the 5.25" disk version for the Commodore 64/128 and comes with instructions, disk and clamshell case. Seller ships to most places worldwide.