Where can I download the 8x8 for Freshdesk plug-in?

You can find the plug-in in the Freshworks Marketplace.

8x8 Work for Freshdesk brings phone communication through a dialer to your Freshdesk environment. The application launches conveniently from your Freshdesk dashboard, allowing you to combine the benefits of Freshdesk with the capabilities of 8x8 Work, and interact with your customers via phone without having to switch to another app.

Upon receiving an inbound call, the app tracks if the caller is an existing contact by searching your Freshdesk contacts, and pops the matching record for you to preview and prepare for the call. This way, you gain full insight into communications with any returning caller. You can be better informed and prepared to answer calls by previewing relevant caller record details before accepting a call.