You can find it locally at places like GNC (or other health/supplement type places). Or Amazon/eBay... brand isn't important as far as I would think with straight colloidal silver, but check the ingredient listings and make sure there's no preservatives or other inactive type of ingredient added that might cause issues.
This would be my first time using it so I'm not sure what is supposed to be in it and what isn't.... if someone could just tell me what they purchased and used that would be great. There are many different brands. Want to know what works.
It's literally just distilled water with silver ions in solution. Not too much to it. For feminized seed making, you'll want to look for colloidal silver that is around 40 ppm (parts per million) - opinions differ on exactly what is the best ppm to use though. And otherwise, just try to find some pre-made that doesn't have any sort of preservative or inactive ingredients in it at all and you should be good to go.
if youre trying to produce "femminized" seeds, gibberalic acid is cheaper, you probably already have some sitting around, it's a common rooting hormone.