I'm just reading Tumah's reply. I don't think it's inappropriate to share this article. I think it is a good reliable source. I say reliable, because the sources are footnoted.
hyperlink >>> etzion.org - Shiur #08: Talmud Torah for Non-Jews
According to this article, the prohibition is discussed in the Talmud. Talmud probably gets it from The Mishnah, not be confsed with the Rambam's Mishneh Torah.
i think it's important to point out that there is a discussion here. If the Mishneh Torah you are referencing is correct: Rambam is giving 1 opinion which is part of a larger discussion.
Another important note about the Rambam: The Vilna Gaon, one of the greatest Talmudic Scholars ever to grace the planet, was extremely critical of Rambam's conclusions. I can find the source for this if you want.
Also... "obligated"... I think "liable" is a better word. But I can look it up if you wish.
The thing is... virtually all of these texts are available online. And I am guessing many of them are supported by Orthodox Rabbis. I find it very hard to believe that Orthodox Rabbis, Rabbis whose opinion you would respect ( presumably, forgive the assumption ) would support the idea that Studying Torah
obligates death for a non-Jew.