Serge Marck has some wonderful period dresses at Poserfashion, although they're mostly formal and none really screams "saloon girl."

Gloria Gast has some nice period pieces over at Poser Junction, also.

Ghastley has a few outfits that might work with appropriate textures, such as the off-shoulder blouse or flamenco dress.

GreyLight has a few Western-themed items (hats, clothes, holsters, accessories) in its Poser Archives.