Not quite what you have in mind, but for consideration until you find what you want: Ive used a strip of belt weight leather with a hole punched at to top for a neck thong and a series of holes cartridge size down it. Just hang it around your neck and pluck a new round as needed. Price -0-
for me; if you dont have the leather, buy a $1 belt at Goodwill, use a shoestring, or whatever and short a leather punch, drill the holes.