I have found a solution, in case it serves someone
The full joystick, we will not find it unless we buy another complete console but that is not the ideal solution, since we always had a console that would not work
The solution is to replace the part of the potentiometer that is wrong.
That is, the bad part of the potentiometer and this part if we can "easily" find it in Aliexpress or elsewhere
In this answer I have put photos of the part to replace
There is a photo of the old part and another image of a new
The joystick has two different potentiometers one of 50k and another of 100k
What we must do is
1) Buy two different potentiometers of 50k and 100k where the part that we are going to disassemble, from the new potentiometers is as the part we will replace. More or less the same size with 3 pins
2) Disassemble the new parts and disassemble the old parts
3) Put the new parts in the Joystick and assemble it again. Keep in mind which potentiometer is 50k and which of 100k
4) Put the cables again and try
This solution will surely also serve, other ancient joystcks from other consoles that we cannot find.