The boards and chips are correct and authentic. From the solder side of the board shown it also looks legitimate.
For the printing on the insert, manual, and cart label it should look like the image is made up of tiny dots when magnified. Ask and see if the seller is willing to take high resolution scans of the front of the insert, manual, and cartridge. When zoomed in you should be able to confirm the printing method.
There would have to be 100s and I'd even suggest at least a 1000 copies of the game world wide. Now subtract ones lost to damage, forgotten new old stock, hoarders of multiples, general collectors and the total left floating around is likely to be far less. But there is no doubt in my mind that there are plenty in existence.