Hi Pluto,
I have reviewed the information available for the *ist D at DPreview.com:
http://www.dpreview.com/reviews/pentaxistd/It is a 6 megapixel dslr that uses the same sensor as the Nikon D100. It accepts Pentax lenses only. It is also the smallest DSLR on the market.
I don't think housing manufacturers will jump to make a housing for this camera, instead focusing their efforts on Nikon and Canon.
With that said, some companies are willing to do custom housings if asked. But on the other hand, why not get a D100 instead? You'd get the same sensor, and a better and wider line of lenses to use.
Cheers
James Wiseman