The only "whole" fabric dealer I know of is Kasuri Dye Works (http://www.kasuridyeworks.com/
I've seen only "scrap" kimono fabric otherwise....
Or try Ebay. I would stick with the Japanese sellers, or stateside: Rising Sun Imports or Yamatoku, for the best buys.
Or you could use rayon-- it was invented as a substitute to silk, after all.... I made my Megumi Takani kimono out of rayon crepe, and it worked pretty well.
For the obi, if can't find obi fabric (or an obi itself, for that matter), you can make one with whatever fabric you wish, just interface it with cotton duck to stiffen it.