Here's silk ribbon from Dharma Trading that's ready to dye:
http://www.dharmatrading.com/html/en...=clothing.html
This is silk ribbon cut on the bias with unfinished edges:
http://www.dharmatrading.com/html/en...=clothing.html
Here's silk cord:
http://www.dharmatrading.com/html/en...=clothing.html
I haven't tried dyeing silk ribbon. I've bought stuff from Dharma Trading and have been pleased with their customer service. I haven't had great results when I've tried to heat-set things with an iron, though. I was trying to do larger pieces, and maybe it works better when you're just doing ribbon. I also haven't used the spray-on dye.
Dharma's catalog has directions on how to steam-set dyes in a pot on your stove. It sounds like it ought to be manageable with silk cord or ribbon, particularly if you're going for a "painterly" effect (and therefore don't mind a little bleeding from one color to another.) Has anyone done it?