This product is either discontinued or we cannot get that from suppliers.
Poly Plantronics 89862-01 Spare Ear Cushions, Black Headset, Leatherette, Poly - Plantronics Blackwire C310, C310-M, C315, C315-M, C320, C320-M, C325, C325-M.
The Plantronics - Ear Cushion is compatible with Plantronics Blackwire C310, Plantronics Blackwire C310-M and Plantronics Blackwire C315.