To install vscode package offline, you need to download those extension by following the resource path as follows :-
Goto https://marketplace.visualstudio.com and browse the extension you're looking for.
You probably get something like this :-
Finally to get our version number we look at the bottom right corner of the extension repository as shown here.
All you need is to fill up the template url above with the right info.
Examples extensions you can download are as follow (might be out of date) :-
John Papa Angular2 extension.
Once you have download it, rename to a more meaningful file name with .vsix extension. And you can install using the menu as shown below :-