Take a look at Crossbill LicenseNoticeAggregator on Github.

The tool iterate through NuGet packages and get the licensing notices in a single file for a product release. It respects the different way the licensing information saved in NuGet package: some of them include LICENSE.txt, some use LicensingUtl tag (with broken links!), some provide README file. Mostly the task can be automated, but a small amount of packages have to be processed manually and put in a tool's directory for processing.

The tool release version is compiled under .NET Core, so can be run on Linux.