I second all of LGJARN52's recommendations, especially Little Red Hen, Fabric Stasher, and Inspired to Sew. And will add -
Heritage Designs in Amana (small, carries lots of batiks)
Fern Hill in South Amana
(don't be thrown off by the gift shop you walk into - it's well worth the climb up the narrow steep stairs)
places I've not yet been to, or it's been a long time -
Prairie Quilt Studio in Urbana
Stitch & Sew and Willow Creek in Kalona (there's also a museum that displays many antique/vintage quilts)
The Woolen Needle and Rainbows and Calico Things in Williamsburg
And if you are coming (or going back home) through Dubuque direction, I haven't gotten to these yet -
Quilt This and Cotton Cabin in Dubuque
The Quilting Tree in Cascade
The Quiltmaker's Shoppe in Manchester
And there's a bunch in the DesMoines area, notably Woodside Quilting which sponsors PBS show Love of Quilting.
The All Iowa Shop Hop is going on until July 31. You might find this useful for finding more shops along the way, though there are shops not participating that you'd miss using only this information -
https://alliowashophop.com
I'd suggest searching for "quilt shops near" whatever towns you will be going through for more complete lists.