I have never bothered with vit C as a topical preparation, but it is do-able. Two words: Kiwi Fruit.
Here is what my formulation dictionary basically says about ascorbic acid, AKA vitamin C.
“Form of vitamin C that has antioxidant properties (Sources: Advances in Experimental Medicine and Biology, 2002, number 505, pages 113–122; and Journal of Investigative Dermatology, February 2002, pages 372–379) and anticancer properties when taken orally (Source: Cancer Detection and Prevention, 2000, volume 24, number 6, pages 508–523). Ascorbic acid is difficult to stabilize in formulations (Source: International Journal of Pharmaceutics, October 1999, pages 233–241). Its acid component is a skin irritant.”
“Topical vitamin C must be in the form of L-ascorbic acid to be useful to the body and skin. L-ascobic acid is unstable and tends to break down rapidly, that’s why it is so difficult to produce for cosmetic preparations. Once it is in the skin L-ascorbic acid stimulates collagen synthesis, provides photoprotection, stays in the skin or up to 72 hours, and prevents UV immunosuppression.”
And, I found a source where they do have a list of natural compounds including, in its raw form, L-ascorbic acid. Problem is, if you want to start messing with a raw ingredient acids as strong as this for your skin, you need to have a pH meter or you could hurt yourself or somebody else.
Having quoted you all this, if you want to make a mask or skin treatment that will make L-ascorbic acid absorb into your skin, mash up some kiwi fruit and put on the area you want to treat. Patch test first. Mix with oatmeal or banana or avocado if the pure kiwi is too strong. It really is that simple.