I think pharmacists usually keep a supply of it. If I ever need any, that’s where I go.
In the chemistry labs at school they used to use ion exchange resins rather than distilling. You may be able to get these on Ebay. Maybe? Alternatively, the water purifying jugs that some people use have an ion exchange resin in them too.
You could make a still in your back garden and do it that way, but the Garda might take some convincing.