Call Nordstrom and ask if they have any denim dresses. Look for something a little sleeker than, say, Dolly Parton wear and you'll be able to wear it again. The belt you bought and maybe a turquoise necklace will be enough to push it into "Western" territory.
Oh, hey, don't know if they have them in the store, but here are some from macys.com:
On sale: http://www1.macys.com/catalog/product/index.ognc?ID=307718&PseudoCat=se-xx-xx-xx.esn_results
http://www1.macys.com/catalog/product/index.ognc?ID=307716&PseudoCat=se-xx-xx-xx.esn_results
Too easy. It's all about attitude. Add hat + boots to a prairie flower print dress the length of your mood. Vintage is your friend. Denim dresses are a mistake.