I am so sorry your Choco is ill. Yes, you are amazing for considering rescue ... putting him first. I would suggest that, while you can look around, you hold out a bit because you don't have a diagnosis yet and perhaps it can be a manageable thing.
What is happening that they believe this may be a shunt? Does he have symptoms? What tests have been done? There are things that can happen with the liver that are perfectly manageable.
There are rescues that you can reach out to, but I encourage you to first find out what is going on with him! (if you can afford to do that). There are groups that can help Choco, but let's see if maybe you don't need to do that first!
I will keep you and him in my thoughts and prayers. Feel free to message me if you need to talk.