As the others have suggested, use a more common part with an adapter and use a flash part to make programming easier. A common trick with old fuel injection computers is to fudge up an adapter made from a couple of ic sockets and a few bits of wire. For the most part, the signals line up, its the extra pins on the top of the device that need to be tied to 0V and 5V as necessary. You can even add some switches so you can have a number of 4K banks on the one larger device. On a 1mbit device, that would give you 32 games in one cartridge.