Invest in a "Quilter's Travel Companion" It runs about $20 I think. It lists every quilt store in the country! Eight years ago, DH and I were taking a trip up the East Coast. We would stop at night and he would take out the map and the QTC. He would say "If we go this route, we can go to this store, and this one and this one, etc" And we did!
Also, when traveling in Lancaster, PA, remember that on Sundays, very few businesses are open!