You have probably hit your brick wall. There is very little possibility of tracking back when they move from one parish to another. The best you can hope for is that they moved a very short distance and look for the nearest parish with a baptism. BUT, this is not proof. Very few parish records for early 1800's give a parents name on a marriage. Sometimes there are witnesses named, which might lead you to a family member, but you may have got back as far as you can.