I shop Amazon all of the time. A shopper can select a charity to donate to with Amazon Smile. I selected Gun Owner's Foundation, a part of GOA, as my charity.
My smile account goes to "Pets N Vets" a local training program here in Indiana (Hebron) that offers free training to disabled veterans for their service dogs.
These people, I can vouch for. I have both PTSD, and a TBI, (IED in Iraq in '05) and took my service dog there every Thursday night (OK, I may have missed a few) for 2 years for training. The entire program runs on donations, and grants, so if you're looking for a cause...