Where can i find (1)halachos relating to maaris ayin, and (2) references in the gemara concerning maaris ayin?
Answer:
This question is a little general, and I will only give brief sources.
The basic source for maris ayin is the Mishnah in Shekalim (3:2), which states that a person must ensure that he does not perform acts that are suspicious in the eyes of others. The prohibition is mentioned in several placed in the Gemara: Shabbos 61b, 64b, 137a, 146b, and a number of other sources; the main sugya is in Bechoros 43b-44a.
See especially Shulchan Aruch, Yoreh De’ah 87:4, concerning cooking meat in human milk (and 87:3 concerning almond milk); see also Shach 87:7; Aruch Hashulchan 16; Chochmas Adam 40:3.
For sources concerning the types of actions that are prohibited (and those permitted), see Iggros Moshe, Orach Chaim 1:96; 2:40; 4:82; see also Minchas Shlomo 2-3:53.
