1) The Shu"t Harambam # 46 says not to standup when the Aseres Hadibros are read.(Ta'arumos Haminim)
2) The Yavetz ,Chida etc. bring the Minhag of standing up for the Aseres Hadibros.
3) The Igros Moshe (O.Ch. 4 - 22) says if your Minhag is to sit and you are in a Shul where they stand
you must stand up. (Minhag Hamakom)
4) R. Y. S. Elyashuv (Shiurei Brachos 12a) Even when in a Shul where they all stand you should sit
(don't get up) because they are all doing against the din ( standing up for the Aseres Hadibros.