You can first try grocery stores and hardware stores, because pure lye has traditionally been sold as sold as drain cleaner. It is great for this because it has NO environmental consequences when poured down the drains. Lye is produced by burning wood, so the environment naturally gets a big boost of Lye every time there is a forest fire. A good brand is Red Devil.
Note: DON’T use Draino, it has additives that cause foaming that will short out your electrolyzer.
If you can’t find lye on your local grocery or hardware store shelves, the next place to look is a local pharmacy. They have access to ALL types of chemicals (though the price is usually inflated) and will be able to order it in for you.
Finally, understand that Lye is used in a LOT of chemical processes and it would literally cripple the economy (similar to suddenly removing gasoline) to remove it entirely. If you search online, you can find wholesale suppliers; and you can usually buy smaller quantities from sources that supply Bio-Fuel and Candle making products.
Here is an example link: Lye and KOH
Since about 2005, Lye has been disappearing from grocery and hardware shelves. It seems that Lye is used to make certain street drugs and, in the ‘war against drugs’ the police are requesting that stores NOT carry it, to make it harder to access for ‘drug labs’.
Taking Lye off grocery shelves doesn’t affect drug labs, because they need LOTS more Lye than that, and buy it from bulk distributors. I still buy my Lye from my local hardware store (even though they have removed it from the shelves) because I have them special order about 30 Kilograms at a time; so much for ‘war on drugs’ argument.
Note: Legal drugs kill far more people than ‘illegal’ drugs. A lot of the legal drugs are just as addictive and have far more side effects. Legal drugs generally treat symptoms, not cure the actual disease (because keeping you sick is more profitable). Vested Interest (in this case Big Pharma) is behind the ‘war on drugs’ because they want a monopoly. They regularly try to get vitamins and minerals classified as ‘drugs’ and they violently suppress any actual cures for disease.
Personally I think this is just another ploy by the Vested Interest (in this case Government tax revenues) to prevent people like you from having access to this (pretty much ideal) catalyst for your electrolyzers. They KNOW that, properly applied, BG technology will reduce fuel consumption at least 25% and that means a revenue loss of billions of dollars per year.