לזכות ר' יהודה יעקב בן דינה חאשע ואשתו היקרה רחל לברכה והצלחה בכל!!
What is the source of the Rambam that Bnei Noach have to keep the sheva mitzvos because they are in the Torah [Melachim 8/11]?
The Gemara says that Kiddush Hashem is אביזרייהו - an accessory, of the sheva mitzvos. How can this be? The sheva mitzvos preceded the giving of the Torah and the mitzva of Kiddush Hashem so how can the mitzva be an accessory when it came much later?? אביזרייהו's come along together with the primary mitzva?!
The answer is that the Gemara understood that the sheva mitzvos took upon a new source after the giving of the Torah. No longer because they were commanded to Adam and Noach but because Moshe was commanded. Together with this renewed obligation comes the mitzva of Kiddush Hashem.
So we have a source that the source of the obligation to keep the sheva mitzvos is Toras Moshe.
In the words of the Rosh Yeshiva ztz"l: