Botanically-focused cosmetics supply vendors will often carry Lye, KOH and CaOH in small or bulk quantities at reasonable prices. Typically these are additive-free and often food-grade due to their intended use being to make soaps and other cosmetic goods.
I won't go naming names, but these vendors can be easily found via an online search. I recommend choosing a vendor which focuses on natural cosmetics and botanical ingredients, as these vendors will often be more upfront about contaminants, adulterants and manufacturing processes. You will typically find more plant oils/butters/extracts, salts and other minerals, rather than synthetic chemicals through these vendors.
These vendors are also great for supplying containers, handling tools, personal protective equipment, measuring tools, and a great variety of highly-potent botanical extracts which open up new possibilities for enhancing your journeys. (For instance, I highly recommend trying *diluted* white Thyme, basil and similar extracts massaged into the skin during LSD trips to combat body load and vasoconstriction)
Biodiesel vendors can often be a great source for things like lye and KOH, if you can find one locally.
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Nothing sparks suspicion like excuses... Just buy your stuff and get out. You won't hear any questions from cosmetics suppliers (especially online), and if you're asked by a biodiesel supplier, etc., just say you're getting into the hobby and listen with interest to their advice.
And don't buy 5kg at a time. That's just stupid... The only reason you need 5kg at once is for commerce, which is not a topic we're here to advise on. Just buy 1kg or less, and secure your stash. No need to go overboard.