Every store, shop, yardsale, or place that offers fabric. I have bought yards of desiner fabric at thrift stores, once at a dollar store in OK on a trip, I bought quality yardage most of it designer signed. Hancock's in No Little Rock is my go to store for quilt fabric. And the larger Walmart stores in AR have yardage of every value, some as much as 12.98 a yd!
Occassionally, I have bought at Hancock's and found Walmart was less expensive on sewing supplies. Their rotary replacement blades are a good buy.
Happy quilting, y'all.