We (Velo Orange) are producing a Mixte frameset in 3 sizes- 51,54, and 57cm. The top tube is a bit longer, intended to be used with handlebars that sweep back.

http://velo-orange.com/vomifrcoso.html

End of January delivery, if everything goes perfect.

From time to time, larger Ross and Schwinn Ladies bikes pop up in the 21 and 23" sizes. but they are not a true mixte design. and they are not exactly performance oriented.