Ok. Well, I have good news and bad news. Did some digging. The standard looking buckles--the ones that go over the twin straps that secure the open main compartment of the backpack in place--are fairly standard, and I can recommend a hardware supplier if needed. That's the good news. The bad news is that the military looking buckles, these:
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were entirely custom milled. If you were hardcore enough, I assume you could have someone here mill them if they had the hardware, or maybe potentially 3d print them and then cast them in metal. There are a few sort of lookalikes if you google "metal cinch buckles", and these almost look like they were taken from a flight or military harness of some kind. I get that the ones from the show were custom made, but the game version, like the watch, presumably had some sort of real world inspiration. I'd like to think something similar exists out there.