I think I have it...in the masonry trade they use a product called "backer rod" that is used to fill spaces. There is a local concrete supply near me that stocks it. I can get it in small quantities, by the foot I believe. I could get some for you if you have none locally. You could shape it and paint it.
measure the diameter near the collar at the base. I hope it's a 1/4". let me know.