You can install either manually or via npm. The latter is very simple:

npm install codemirror-find-and-replace-dialog

Add the following imports.

import "codemirror-find-and-replace-dialog/dist/search.js";
import "codemirror-find-and-replace-dialog/dist/dialog.js";
import "codemirror-find-and-replace-dialog/dist/dialog.css";

Obviously you need to include CodeMirror in the page. You also need to include addon/display/panel.js from the CodeMirror default installation.