Where can find the Iggeret Hashemad of the Rambam online in English? There are lots of scholarly resources talking about it, but I am unable to find the words of Rambam complete in translation.
This letter of Rambam was translated into English by Leon D. Stitskin, and published in Tradition in two parts. The first part was published in Vol. 16 No. 4 (Summer 1977) under the title "Maimonides' Maamar Kiddush Hashem" and is available in the archives as a PDF here. The second part was published in Vol. 14 No. 2 (Fall 1973) under the title "Maimonides Letter on Apostasy" and can be viewed in the archives as a PDF here.
You can read the translation (with notes) of Prof. Abraham Halkin (‘Epistles of Maimonides Crisis and Leadership’) here. The translation is then followed by discussions of it by Prof. David Hartman.