Doug, the Rio Grande Catalog has 6mm I.D. 14 gauge sterling rings in
packages of 50 for 15.03 ea, cheaper at volume, 'bout 11.00 each for
over up to 19. You could probably call them for a better price at
that quantity.
Rio Grande, 800-545-6566
6mm sterling jump rings, 14 gauge, part number 693-614, page 301 in
the new findings catalog.
Don’t know about the 12 gauge, but maybe chain manufacturers would be
able to make or sell you something like that. If you would like that
info, please email me.
Good Luck,
Andrew