I belive that there are 16" Vitara rims. Suzuki 4X4 wheels bolt straight on. Also early Lada Niva. And the very eirly Daihatsu Taft wheels were 16". These are very narrow, and like hens teeth to find.
The best bet is to ring all the 4X4 mag shops and ask if they do them. Some do. Also specalist wheel co.'s will make any sive you want. Expensive!
Personaly I would stick with 15". There is more choice of tyre anyway.

Any veiws expresed in this thread by me are purely from my own experience, and (sometimes) falible memory. Hope my comments help, but please don't take them as gospel.