According to Google, “to protect you while you browse”, Chrome only lets you use extensions that have been published on the Chrome Web Store. But if you want to use any extension which is being unpublished or removed from chrome then you need to manually install them.
Here are the steps to install/unpack chrome extensions manually using the CRX file.
Step1. Download the CRX file for the chrome extension you want to install.
Step2. Go to the setting and then extension, or visit chrome://extensions/
Step3. Turn on the developer mode from the top right corner and click on load unpacked then locate your extension folder where CRX file and the main file of the extension to install it. (you can also directly drop CRX file into the extension page)