PFLAG is an amazing national (international, really) organization that supports parents and other allies of queer and trans people. This is the same organization to which i'm donating 50% of the proceeds from merch sales -- that's how much i love them.
Check out their website to see all they great things they do.
First, see if there's a chapter already in your area. If there isn't, consider visiting a nearby one and talking to them about what starting a chapter entails.
You can also become a PFLAG member.