It all starts with the classic Revell Aztec set, which I used extensively for the Aztec army. However, the figures I had included quite a few of the two archer poses, which I did not end up using. In a fortunate coincidence, I noticed that the DBA army list for the Tlaxcalans calls for large numbers of bow units. After counting out the figures I had, I realized I was a little short, so I looked around for some plausible substitutes among my collection and have come up with some that I think will do the trick. Here I have everyone counted out and mustered into approximately the units that will be required:

I also did some digging around for visual sources, and was pleased to find mention of a work known as the "Lienzo de Tlaxcala." The Tlaxcalans ended up more-or-less allied with the Spanish when they arrived, and after the Conquest, this document was put together to depict the Tlaxcalans and their new friends getting together to beat up all their neighbors. It is laid out almost like a comic strip, with most of the panels showing the Spanish and their allies fighting various native peoples (whose origins are helpfully labeled:)



(images courtesy of Manuel de Yáñez, Public domain, via Wikimedia Commons)
As you can see, there is quite a bit of material to work with here as far as costume, weaponry, and shield designs. (The colors I am still a little unsure about.) My next step will be to do some conversions, hopefully ending up with some figures who are a bit closer match to the warriors depicted in the Lienzo!