Oh, my friend, you have come to THE big problem of transplanters : the pots!

Alas, the answer to the million dollar question is : I MADE THEM. "Oh my god", you think. And you are right. Just two pictures to make it clearer :

The pots I used to make the ones of my 1rst post :

BTW, some choices were stupid : the pot chosen to shelter the volume control was with a "center click", which means that you feel a stop when you reach the middle of the pot's turn. Useful for a balance pot, useless for volume. I would choose other models if I had to redo the whole thing (but hell I don't want to do that AGAIN).

And what it looks like with all parts... apart :

After, you much equip with a tool to verify that your pot is still working after you replaced the plates (the green things), and then glue the retaining rivets you had to cut in order to dismantle the pot. Be very careful when you do that with the stacked pots : always keep in mind that you will have to put everything back together.

The final pot, gluing the rivets :

My english not very good either : I'm a poor frenchy rookie trying to build his first transplant. And progressing VERY carefully.

In order to end up with a positive tone, I heard that these guys can make custom pots. But it will cost you more than what it's worth. Or not

I think that I will contact them for the next transplant (OMG, I can't believe I have said "next transplant" although the first one is not over yet : I must be sick)

Oh, I forgot to answer your 2nd question : the specs.

For a Variax 300 transplant, you need :

a volume stacked pot with :

• 2x10 lin plates working together that will be wired on the Variax motherboard after you remove the original stacked mini-pot
  
• 1x500k log plate if you use at least one humbucker (or 1x250k log if you use only single coils) that you will wire as if it were a single volume pot in a standard guitar
  

a tone stacked pot with :

• 1x10k lin plate wired to the Variax motherboard (remove the single mini-pot) if you transplant a Variax 300. If you do it with a 500 or 700, you'll have to take a 47k lin plate
  
• 1x500k lin plate for humbuckers (250k lin for single coils).
  
• a push pull switch (DPDT On/On)
  

That is what you need. Let us know what you did