Yes, it would be possible to manufacture new system cards,
Indeed. It might even be possible to make a system card with more than 128K. Or even.....
Well, I'm not allowed to talk about that.
As for an arcade card duplicate? Possible, but not likely. There is apparently some unknown circuitry (ie, no one has bothered to reverse engineer it) on the arcade card. You could possibly duplicate it with a fpga, but it would take a good bit of work to do. Personally, I'd rather figure out how to expand the mmu for more directly acessable ram space