The first link that google came up with was for here to buy the dye: Dharma Fiber Reactive Procion Dyes
I'm wondering how it'd work on silk flowers? Since I'm pretty sure it's not the same silk they are referring to (or is it?) in what kinds of fibers it works on:
All natural Fibers (Cotton, Rayon, Hemp, Silk, etc.), Wood, Cane, and Rattan
ETA: It would be awesome if these did work on silk flowers. The color chart is AMAZING!!!!! Scroll down on the above link and you'll see all the many colors they have!! How fun!!
Also found this: How to Dye Silk Flowers & Feathers Using WashFast Acid Dyes
Ok, I read around some more on google and apparently just because one dye works on REAL silk (not polyester, which is probably what your flowers are) doesn't mean they'll work on the polyester ones. HOwever, this website has some paint that they say works on both. Jacquard Textile Colors - BLICK art materials