I have purchased sterling foxtail chain at Myron Tobak, Inc.,
which is located at 25 West 47th Street in New York City
(212-398-8300). The chain I purchased was very thin (about 1.5
mm.). I didn’t notice what other sizes were available.
Metalliferous (34 West 46th St.; 212-944-0909) sells handmade (I
believe in Bali) fine silver loop-in-loop chains (including
doubles, quadruples, and a couple other variations which are
very nice). They are sold by the gram.