SOME wood stove glass cleaners contain lye
There is lye in a number of drain cleaners - they sometimes put other stuff in too though because evidently lye gets used for making meth? Idiots.
Lye can be had from soap making supply places/companies
Red Devil is a name brand of pure lye.
Lye is Sodium Hydroxide but often Potassium Hydroxide is used instead.
BioFuel can be made using Potassium Hydroxide and Ethanol vs. the more dangerous Sodium Hydroxide and Methanol (nasty stuff).
You can MAKE lye from wood ash. It may contain Potassium Hydroxide (perhaps that works too?)
One way that would probably work is get a poly bucket or barrel, fill with wood ash, have tiny hole at bottom, let rainwater or distilled water drip through the ash. You can concentrate the solution by boiling in a NON METALLIC CONTAINER but really do you want a pot of boiling lye around anyway?
I have vinegar on hand to counteract the lye on, say, my skin any time I use it for anything (assuming I can't just immediately rinse with a LOT of water).
If you've never used Lye, read up on it first. Chemicals are tools and just like most tools they can help you a lot, or maim/kill you.