As of February 2015, Amazon.com sells blender replacement gaskets, and so do independent parts retailers such as Appliance Parts Pros. Some blender manufacturers, including Oster, also sell replacement gaskets and other parts through their official websites.
Amazon.com also sells a six-piece Oster blender refresh kit, which includes the gasket. It comes with a filler cap, ice crusher blade, two sealing rings and a lid. Appliance Parts Pros sells individual gaskets.
Shipping is free on Amazon.com with a minimum order totaling $35 of merchandise, not including items sold by third-party vendors. Oster offers free shipping on orders of $50 or more, and Appliance Parts Pros charges a flat shipping rate.