I discovered that a clam shell makes a fabulous pin holder. We call them Quahogs in the New England area; they are a chowder clam or in the rest of the country a medium size shell version are called "Little Neck" clams.
They have a natural balance point so the pins do not spill out over your table, it gently rocks them to the center.
I've used them for more than 25 years and spoken to many people in many sewing spots, but you are the first person to really show interest in the possibility of a self-balancing pin holder from Nature! The oval ocean clam shell makes a great soap holder as well as those Daisy headed pins.