I was thinking about my collection of AA Mini Mags, and I have two I don't see in your collection. Back in the late eighties or so I acquired a gold AA Mini Maglite. It's not the bright gold like you have; I have one of those. It's a darker color. Not as dark as the bronze color; I've seen one of those. It's just sort of a darker, duller, less brassy looking gold color. Around the same time, I also got a silver AA Mini Mag. It's like the gold one: a darker, duller silver than the current silver ones. I have no idea where I bought them; probably mail order, as they weren't very common back then. I have no idea if they are rare or not, but I find it curious that the management at Mag Instruments didn't know about them.
Good luck finding a 18K gold plated one; I have a feeling they don't come up for sale very often. But perhaps if you check eBay every week, with a structured search to screen out as many false hits, you might find one, sooner or later. I hate to think of what the price would be, though!