We have a web app project that still uses NuGet for content packages management (jQuery, Knockback, knockoutjs, etc.). We are trying to convert to use LibMan, and running into an issue where some older packages do not exist (for instance walltime-js). How do we work around this issue?
Try using a different provider. The current default, Cdnjs, is a curated catalog; the other two providers, JSDelivr and Unpkg, host any package that's available in NPM and thus have much broader catalogs.