babyiwantabump I got my stuff off Amazon. The Vitamin C (L-ascorbic acid) powder I got was this one:
www.amazon.co.uk/gp/product/B00D1PSLB6?psc=1&redirect=true&ref_=oh_aui_detailpage_o03_s00
Holland and Barratt carry it but I don't know if the crystals are very fine. The stuff doesn't dissolve very easily so the finer the powder, the better. Some people use a little mortar and pestle to grind it down even further.
Boots carries less and less actual chemicals. You can't even get rubbing alcohol from them any more. But another chemist - a proper chemist - may well carry distilled water and vegetable glycerine. I got them off of amazon which was probably not the cheapest way to go. Having since read this, I realise that for this purpose, deionized water is as good as distilled:
www.distilleddeionizedwater.com/deionized-water-vs-distilled-water/
And you can get deionized water from Asda or anywhere that sells basic car care stuff (it will be by the car wax and motor oils) because it's suitable for putting into radiators or batteries or whatever one does. It will certainly be cheaper than paying to ship a bottle of water ordered on Amazon as I did.
The final thing is a blue or amber glass bottle. Easily ordered on Amazon. I further shield the stuff by putting the bottle in a child's sock but you can just pop it into your medicine cabinet away from light.
If you can get deionized water and l-ascorbic acid, and a brown bottle, you're good to go. The glycerin is an optional extra that isn't really necessary, but some people like it. I find it makes my face feel tacky and I won't be putting it into my next batch.