What is the best store to find GOOD duvet covers?

I painted my room a deep purple and have gray furniture. I need a good duvet cover that'll match. I really want to find one that is white with some sort of purple design (flowers?). But i've looked at ikea, bed bath and beyond, macys, jcpennys & Sears and none of them had a good selection. Are there any other good stores. thanks.
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duvet covers