Using SharpGL Source Code Offline

Forgive me for asking this kind of question here out of frustration, but I use SharpGL within an organization where we are required to do all development work offline (no Internet connection), and I need help.

I'm trying to use the latest version of the SharpGL project (3.1.1) downloaded from github, but it is tied to the new "dependencies" way of defining relationships (vice using References). Attempting to use the code in my project now yields the message "Error occurred while restoring NuGet packages: Unable to load the servcie index for source https://api.nuget.org/v3/index.json." Obviously this is because I'm offline, but certainly the SharpGL project (via .NET's dependency methodology) doesn't expect you to be connected to the Internet just to compile source code, right???

Again, sorry that this is a more general question about compiling projects with dependencies (vice References) offline, but SharpGL is the first source code we use where I've run into this issue. As a developer who has contributed code to this effort (and I continue to make modifications to the source code that I may find useful enough to share in the future), I'm hoping I've gained some credibility here and some kind soul will offer to help. Thanks!

The issue names SharpGL 3.1.1 and the NuGet source https://api.nuget.org/v3/index.json, but no files or tests. Reproduce the restore failure in an offline environment, then determine and document the supported way to build SharpGL from source without network access. Done means the offline dependency workflow is clear and verifiable.

Written by the indexing model from the issue text.