Explore the western forest for the potions. I'll add some signs warning you not to go there so its a little more obvious. [...]
Gender change potions won't work on the goblins for the lore reason of the "god" the goblins worship has done something to their race already and nothing further can be changed.
I kind of spaced out on this question before, or I would elaborate. The reason why I asked about futa potions is because of this line in the 1.5 changelog:
* - Goblins are correctly now immune to gender change potions as intended, but not immune to futa potions.
I interpreted this line to tell me two things: a) there are futa potions in the game, and b) goblins are not immune to them.
For the point a, the only potions I can buy from the witch in the western forest are the ones that turn the drinker male or female, but none that turn the drinker into a futa, so I wondered if these potions are not yet in the game or if I simply didn't find them.
For point b, well, it says that goblins are not immune to futa potions so I assumed they could be used on female goblins (like the goblin wife) to turn them into futas, either in the current or future builds of the game.
I would appreciate clarification, especially if I misunderstood something.