I don't know how useful this will be, but orthodontists use small, circular rubber bands to move people's teeth around in their mouths. These come in about five different thicknesses/strengths/diameters (the stronger ones have smaller diameters). These are sold in bags of fifty to one hundred for five dollars or so per bag, but the only places I know to buy them would be directly from an orthodontist. A medical supply house might be able to help, and I have had women in Ontario and Austria tell me that they are commonly available (at drug stores?).

A BDSM advice site (whose address I have lost) had an article on nipple exhibitionism in which the author indicated that 'nipple teasers' were available from big city sex shops. These sounded like little neckties (or nooses) with adjustable sliding knots and are meant to be worn under sheer blouses, as nipple jewelry.

If anybody has any further advice or information, I'd be happy to hear it.