Yarn woes

Where oh where can I get a nice cotton or bamboo in bright rainbow colours? I have been searching every wool shop I know and scoured the Internet and I can not find one range of yarn that has all the basic colours and really nice bright rainbow colours without it being a nasty acrylic bargain basement one.
 I've never been fussed about using all the same make of yarn when I'm making something as I think amigurumi is quite forgiving and you can pretty much get away with using any DK weight.
 Now I'm trying to get a bit more professional with my patterns I have a chance of getting them in magazines and maybe even a book but this means I've gotta make sure I include the information about the yarn and material's I've used, and I don't think anyone would be too happy to discover I've used a yarn from my stash that's 10 years old and no longer being made.
So if anyone has any ideas or have seen a good range of yarn somewhere out there please let me know.