Even if you can find the dye somewhere, you'd probably have to dye the clothes white first or bleach them, so the blaze-orange would have a workable base. Putting blaze-orange over a drab or dark color isn't going to do anything but make a dark, rusty color.
You might want to just look in to a cheap Wal-Mart type all purpose blaze orange vest, usually found for about 15 bucks, to slip over your hunting clothes. Seems like it would be a lot easier than bleaching, etc etc etc....
Good luck.