My mother does charity quilting for Lutheran World Relief where the standard quilt size is 60x80. She gets sheets donated from a Holiday Inn. Sometimes they just have a little tear in the corner. Since they are all white, she dyes the sheets (with Rit dye that I find at estate sales). Any sections that are thin/worn she cuts into 10" squares for foundation for my string blocks.
The Holiday Inn also donates banquet tablecloths, which she usually uses for filler in the quilts.