This page (https://support.anker.com/s/article/Introduction-to-Anker-2-4G-Wireless-Vertical-Ergonomic-Optical-Mouse-Receiver) is active as of today and says:
"If you are located in the US, please contact Anker customer support with your shipping address and model number of the mouse, our Anker customer support will check in our warehouse if we have replacement receivers for selling. "
