From my limited experience...
Gold plated means that it won't tarnish so you would be looking for protection from scratches rather than from the air, so you probably don't need them to be airtight.
I looked into getting some clamshell packaging made, similar size.
Custom vacuum forming mould $3400-$3800 approx
Die cutting knife $220- $380
Then you need to add the cost of the actual clam shell, for which they want a minimum order, around 1000 from what I can remember.
They expect you to add the cost of the clamshell to whatever product you are selling so you can pass the cost onto the buyer.
You kind of figure that you could use some yourself and sell the rest, but here is the kicker, the company would retain the vacuuforming molds and reserved the right to sell your product along with their own. So any thoughts of selling the remaining items as a business would have to take into account that there is a plastics manufacturing company who can sell them cheaper than you can and they haven't had to pay any of the set-up fees.
I gave the whole thing up as a bad idea but I might revisit it now that 3D printing and 'makers' are taking over from the larger companies.
I also got in touch with Ultra-Pro with the idea but they never got back to me, they might be able to help you though, or Lighthouse, they both have archival quality storage solutions for things you didn't even know needed storing.