If you really are dead set on donating I would wait until someone actually needs it for legal defense I would not trust any org.
You mean actually donating to an actual person who is involved in a law suit as a plaintiff? I would not know where to find such a person now would I have any means of verifying that it's not a scam. Plus I think money donated this way would not have the same effect as when it is donated to a bigger organization like the GOA or SAF.
It's like with PETA; I am not big on it, but I do donate money to it recurringly. if I had simply donated money to individuals who advocate for animals, my money would have very limited influence/effect. But when I give to PETA, they can pool everybody's donations and try and lobby for laws to be changed. it's the same principle.