I saw someone wearing some clothing that is not in the campus store. Like Sleeveless shirt and some t-shirt have the faculty name. Where did they get from? Thanks.

Prob ordered directly from the faculty

Some of it could be from the MaroonShop in DBAC, but most likely what you are frequently seeing is clothing that each faculty or student society (ex. the DeGroote School of Business may order them for commerce students/staff or the DeGroote Commerce Society may order them just for commerce students).