Sadly, I think even our longest lens, a 14", would only be appropriate for an 8x10. A diopter lens (usually sold as a "close-up" attachment) might do well for you. I've used these quite a bit with my own home-made concoctions. The main thing to know is that a +1 diopter is one meter's focal length, a +2 is a half meter's fl, a +3 is a third of a meter, etc. A pair of +1's or a single +2 should be about right for 11x14 portraits. The lenses are additive, so two +1 lenses equal a +2, a +1 and a +2 equal a +3, and so on.
The aperture placement determines field flatness and coma, but spacing and maximum aperture are the "fun" things to play with. But the actual lens itself you just have to live with and work with. But I've made several, and love them all.
Here are some images from my APUG gallery made with multiple-diopter lenses: