I don't know much about Des Moines but there is one right in "old town" Ankeny and I don't remember the name. If you get a chance to go north Ames has "Quilting Connection" at the corner of Main and Kellogg. It is packed with material and friendly clerks.
The about 7 miles east of just outside of Nevada is Block Party Studios, Inc. They have lots of specially printed sayings and labels.
Those are the 3 I go to the most.