Make my own, of course :)
I've been making this for little over a year, mixing a fresh batch once every few weeks, and I still haven't had to rebuy the ingredients, which cost less than one over-packaged bottle of the premade stuff.
Improve your complexion on a dime:
Add 1/4 t l-ascorbic acid, 1/2 t propylene glycol (or glycerin if you have very dry skin), and 2 t distilled water to a blue or amber bottle. Shake vigorously for a few minutes, then shake a couple times an hour until the powder dissolves.
This will give you an approximately 10% solution. If you have sensitive skin, or are in doubt, cut back on the l-ascorbic acid.
Do not double the recipe. Vitamin C can become oxidized as it sits and may cause free radicals to form. It' s important that you mix a fresh batch every few weeks. I keep mine in the fridge.