Here is an 1800's dress from MTS2
http://www.modthesims.info/download.php?t=203467as well as mariachi outfits (although you might be looking for something a little bit more ornate)
http://www.modthesims.info/download.php?t=327684.
I don't know if you've checked there already, but the Prarie theme at All About Style has some really beautiful stuff, including some indian clothing.
http://www.all-about-style.com/themes_prairie.html Definitely old west.