The theory is that dysfunctional muscles in the neck and along the vagus nerve affect the function of the gallbladder. Sometimes there is a trigger point in one of the muscles that can be released by massage or exercise. Some people opt for acupuncture but most have to find a solution themselves.
If you search for "gallbladder meridian stretch" it will take you to some videos of stretches that you can try. Searching for "Gallbladder trigger points" will take you to a number of interesting articles which will explain the relationship between muscle knots in the muscles call trigger points and the digestive system.
If you want to buy gold coin grass in the UK it is often called Jin Qian Cao or Lysimachia christinae. I have used Bristol Botanicals in the past.