Like many folks who are gamers of a certain age, I first learned of M. A. R. Barker via Empire of the Petal Throne (1975), a roleplaying game published by TSR not long after the early success of Dungeons & Dragons. My own DM for D&D, which we started playing from the get-go, had dibs on a lot of published RPGing materials but wasn't interested in EotPT, so I grabbed a copy myself. I think I was too young at the time to appreciate the great depth of the system but lifted some ideas for D&D games that I ran when our regular DM was taking breaks from time to time.
M. A. R. Barker put out quite a bit of material in his lifetime, much of it for his own setting of Tekumel through his RPG but also for wargaming. When Gary Rudolph came out with his Missúm! (1978) wargaming rules, he worked with Barker on a six volume series or army books beginning with The Armies of Tekumel, Volume I: Tsolyanu (1978). Barker continued working on the series on his own, at first, and then with Bob Brynaldson for the final four in the series. Toward the end of the series run, Barker worked with Jeff Berry on the Qadardalikoi (1983) rules which could also use the series of army books and which was specifically meant to be able to conduct wargames in the world of Tekumel.
Now, The Tekumel Sourcebook has been released as a "reprint of the original Gamescience edition, with" a number of "changes and additions" that fans of the setting should really enjoy. Check it out here.