The most practical would be to get two adjustable ones ( single channel )
And make a third of your own, combining many LM7805 / LM7806 / LM7812 ... up to 24V or more.
Ok, adjustable with DAC and two buttons for reference source. Potentiometers tend to wear out producing dangerous pulses at output. Mastech produces something in that range but there are no dealers at all.
Ok I have one last suggestion and I believe that is usable.
Start using the ebay.de link, there is a true wide market in Germany (that is almost close to your door.)
Make a list of some branded models that you have some interest, and I will personally help you, to locate one of them in the German ebay.
My own Kenwood supports remote control operation, and master slave operation.
With out knowing it, you gave me an wonderful idea , to use the remote connection of it, in a way to have selectable presets,
instead of rotating the knob all the time.
And so I can use it, as to was programmable but with out any software.

( I will make an complete presentation about it soon )
And so I am ready to return the favor, when ever you are ready too.