If I liked you I would tell you great places online to buy fabric, but I don't like you so I won't.
Obviously, I don't sew, but my mother loved to.
I haven't noticed, myself, the decline in selection of fabrics in retail establishments, although admittedly I don't pay much attention. It seems to me the area Hobby Lobby store carries a vast range and quality of fabrics, and they seem to sell a lot of it.
My only experience with this sort of merchandise was that when my younger brother and I were little, and didn't have much money, every Christmas, we went to the local five-and-dime and spent a long time looking at, and selecting from "Simplicity" dress patterns, and then selecting the fabric suitable for the pattern. That was our annual Christmas gift to our mother, a new dress (of course, she had to make it herself).
Does "Simplicity" still exist, by the way? They used to be really popular.
Sometimes the saleslady would arch her eyebrows at my brother's and my selection, and gently steer us towards something more appropriate for a middle-aged matron. As we wished to please, we took her suggestion rather than ours. Also, we had the habit of initially selecting a dress-pattern some sizes too small.