Tripod help - a mount with a socket that attaches to a ball?
It seems like you're talking about a quick release plate. The problem is not that plates don't exist, the problem is that they may not be one that fits into the head of your existing tripod. Most tripod manufacturers use a proprietary shaped quick release plat. The exception to this is Arca Swiss. There are several tripod manufacturers such as Really Right Stuff, that use the Arca Swiss style of quick release plates. Tell us the make and model of your existing tripod. You explain what you're looking for, but you really don't explain what you're trying to do. Maybe I'm a little dense because it's early and I've not had my coffee yet? What I do know is that if the piece you're looking for exists, then B&H will have it. Take a look at their tripod accessories page: https://www.bhphotovideo.com/c/browse/Tripods-Support/ci/8310/N/4075788771 Manfrotto (formally Bogen) makes a boat load of clamps and tripod accessories. They may have something that is different that what you have in mind, but will do the job.