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It's interesting how you mention that folks outside of South America wouldn't really know about this conflict Blucher. I'm American, but my wife is Bolivian, so it was only through her that I discovered the Chaco War, which unfortunately went very badly for Bolivia (as have most of their wars). You're right, there's probably not a huge market for this, but if Strelets were to do some limited edition sets I would certainly pick them up.
Would also like to see the MK5 . As to it not being viable commercially strelets has covered some pretty obscure conflicts already . The Russo Turkish war with I think 12 sets springs to mind .2 sets for the Chaco war seems doable especially as they will be the only ones in the marketplace
The South American wars of independence might also be interesting. Would love a set of Bolivian line infantry in red! I don't think we'll ever see them, though as many other sets from similar time periods can be pressed into service here.
this article gives some background info and may be useful as an overview for arms, the Vickers Archive also has a number of photos of guns intended for this conflict...