Anyway, on to the specifics.
Firstly, I bought another book on the Chaco War - The Chaco War 1932-1935 - by Antonio Luis Sapienza and José Luis Martínez Peláez published by Helion. Helion have a prodigious output. They also overwhelm you with marketing emails which I was about to cancel when I saw this title. The book is nicely illustrated with contemporary photos and some coloured illustrations, and is a worthwhile addition to my collection.
I've taken an interest in the Chaco since Khurasan launched their 15mm range. There are also plenty of vehicles available in that scale. I own that prior to that I'd never heard of it. I like the Chaco War because it's offbeat and obscure, and I'm particularly attracted by the 'quirky' interwar tankettes, but these were used in such small numbers that I could really only justify their use in a skirmish-level game.
Here I think the most promising option might be Chain of Command as this would allow for tanks and all sorts of other assets - HMGs, mortars, field guns, trucks etc - all fielded in penny packets. Using CoC for the Chaco was discussed here.
For those seriously interested, a great collection of links to Chaco War resources can be found here.
For 'mass armies' I remain more inclined to 10mm, but there's no sign of that happening and 15mm is at least a step in the right direction. I'll stop there. I'm not hitting any 'Buy Now' buttons. Well, not yet, anyway.