There is precious little in the way of 7800 accessories, as many in planning and development were cancelled. I'll put any I find, here.

This controller sure takes the "joy" out of joystick. The Atari ProLine Joystick must have been designed by goblins or extradimensional horrors with non-Euclidean appendages. It is in essence, a narrow rod with a stick protruding out of it at a right angle, with buttons on the left and right sides. This controller was apparently tested by nobody, if not the fantastic monsters that designed it, because wrist and finger pain sets in within minutes of playing Xevious, Choplifter, or Ball Blazer. It is an utter abomination.

I received a strange box in the mail, and it contained some baggies full of resistors, some plastic NES controller pieces, an amazing bright blue circuit board, a weird plastic sheet that looked like it was made from a strand of plastic, and a DE-9 cable. The instructions said that this assemblage of parts could be used to make a Sega Master System controller, or an Atari 7800 controller. Given that the ProLine controller is absolute garbage, I elected to follow the Atari instructions. After I epoxied the plastic label onto the controller shell, I tested it out. It worked perfectly! I tried going to the website in the instructions, but I got a 404 error. I think I shouldn't dig too far into this, as if this is some sort of alternate reality stuff, I'll just consider it to be good fortune and leave it at that.