I am not entirely sure which type of silk is appropriate for Kimono's, etc., but Fabric Depot (SE 122nd and Stark) has a very large selection and if you look in the Sunday paper, or get on their mailing list, you can get coupons for as much as 50% off on a cut of fabric...... which is a good thing, because silk can cost anywhere from $18 to $100 a yard. A cheaper alternative might be rayon or cotton prints. I have made kimono-like garments before and can make it look good, but I don't actually have the skill to make one 100% authentic. There are some pretty good patterns online if you just Google "kimono pattern", I had more trouble when I looked for a good hakama pattern, however.
If you are interested, I know a second hand store that has real kimono's from Japan in stock.