The French national library has been scanning a lot of material throughout the years, available on their website Gallica. Using their advanced search tool we can narrow down to works in Latin about mathematics: here is a direct link to that query result.
Similarly on archive.org, by finding the collection on mathematics and narrowing down to those written in Latin one can find the following material.
In both cases however it should be noted that all material is from 1400 to 1900, I didn't see anything older than this unfortunately, so no ancient mathematicians there. Euler, Descartes, Huygens etc. however all wrote in Latin, so one can find their work at both those links. A couple of ancient Greek mathematicians are translated in Latin there, but the translations are all from the 18th/19th century.
Edit: I also found this website that contains a lot of ancient mathematicians' works, some of them translated in Latin, but, again, those translations (as far as I can see) are all post-15th century.
