¡Hola!
Do you know the set of expression "If it's not broken, don't fix it"?
If you absolutely want to change it, any old conga skin will fit, as long as it's not broken, worn, nor too thick. I suggest you to measure the thickness of the original one to see if you can find something similar. Try to find a conguero in your neighbourhood and ask him/her.
If you can't find any, try horse (thicker than for the macho) or cow, bull, whatever you can find. My motto has always been "Play what you can find/afford".
The choice of the animal depends on personal tastes : some prefer bleached cow, some swear only by mule, etc. And some want synthetic (matter of taste, climate conditions and practice)
These are just my 2
centavos :) , maybe other members will suggest you something else.