This product is either discontinued or we cannot get that from suppliers.
Poly Plantronics 88817-01, Material Foam, Ear cushion, Compatible With Poly EncorePro HW530, HW540, Black.
The Plantronics replacement cushion # 88817-01 (Sold individually) is an individual ear cushion, which includes an affixed rubber ring on the inner side of the cushion and simply slides onto the speaker of the headset.