In brief, I would like to know if there are any good spots in Might & Magic 3 to farm gems. I want to do that, just for a bit, to save up enough to boots some attributes from Lord Might's crystals in the Arachnoid Cavern.

I heard somewhere about farming the wizards in the evil castle by failing to open the riddle chests (that are also locked) over and over, but I tried that and, while the wizards do drop a nice amount of gems on each kill, they would only spawn for me when I would properly open each chest, so it wasn't something I could do ad infinitum.

I don't want to just edit in the gems - I want to earn them even if it's rather "gamey", so any suggestions would be welcome.

In Castle Blood Reign (it's the neutral castle) you get asked about the former name of frozen islands, if you answer the code the alarm sounds and the wizards (doing cold damage) spawn. When asked who will open the chest select a non-thief (don't remember if pressing the escape key works), he will fail, the chest stays and you'll find some wizards to kill in the castle.

Another (but slower) option is going to the island where the sprites are, there's one location where you only have to turn around a few times in order to make some respawn at 2 squares distance.
Or you can simply press the gongs in the spider cave to lure some spiders out.

The easiest way is putting all your gems on the bank, they'll increase fast.