Check discount places, and even department stores - and don't forget to look at the men's racks. Especially as, for some reason, often the strong or bright colors for shirts don't seem to sell well to large men, so you can often find "dress shirts" that would fit you, but in colors no self-respecting guy would wear. You just have to get used to them buttoning on the other side, and maybe put in some darts to emphasize your girliness, that's pretty simple to do.