If you want to get suitable shooting glasses frames for your large head, you can just choose the big sized shooting glasses that match your large head. If you don't want to drive around to look for it, you can search it online. But you must know what the size of shooting glasses you need that to help you choose suitable glasses frames quickly. And you can rudyprojectusa.com where offer many types of shooting glasses. Hope this help.
I also have the same large head as what you describe and have had my best luck with Oakley's M-frame wrap arounds. It has Wide frame, comfortable nose piece, You can bend the nose pieces in any direction until you get it to fit right. They might work for you. Hope this can help.