Wow. That's a pretty interesting, old kit! I guess you'll have to haunt ebay for the chance that one will show up.
That MIM one is Lunar Model's kit. I just ordered it from LM directly as few months back. It's not the state-of-the art in model design (come on, it came out in the mid-80s!), but it's perfectly buildable. I talked to Randy, the current owner. He'dfixed up the model so now it's an all-resin kit. He's a good guy and quite earnest about replacing any defective parts to any Lunar model kit that he has the molds to. If you're looking to get a nice GK of the Ark, that's the place to go.