Well, there is nothing for the general store in our debugger we use to fix saves, so that's why we can't unlock it. It is actually unlocked as soon as you go to the map when you first start exploring the area. The missing general store location would have been sometime around version 0.7x, so if your save is that old, that's why it's missing. Any saves prior to that version will run into this problem.
And the reason the saves are encrypted is to prevent players from tampering with the saves. This caused nothing but problems in MotH (missing hints, incorrect hints, unable to progress the storyline) because of that very reason and we were not going to fix any saves that were tampered with. I, personally, had ran into one player on Discord who decided to make in excess of 1,000+ changes to the flags in his save and they still expected support for it even though it was by his/her own doing.