The service index is the entry point for a NuGet package source. Looking at the document the SearchQueryService has the comment Query endpoint of NuGet Search service (primary) that supports package type filtering and is avalible at https://azuresearch-usnc.nuget.org/query which seems like it will work for my application.
Search Query Service
The package log4net felt like a good candidate to pick on:
{ "data":[{ "id":"log4net", "version":"2.0.14", "description":"log4net is a tool to help the programmer output log statements to a variety ....", "totalDownloads":107054643, "versions":[{ "version":"1.2.10", "downloads":5725024, "@id":"https://api.nuget.org/v3/registration5-semver1/log4net/1.2.10.json" },{ "version":"2.0.0", "downloads":2961996, "@id":"https://api.nuget.org/v3/registration5-semver1/log4net/2.0.0.json" }] },{ "id":"Microsoft.ApplicationInsights.Log4NetAppender", "version":"2.20.0", "description":"Application Insights Log4Net Appender is a customer appender allowing you to send Log4Net log messages to Application ...", "totalDownloads":7938163 }] }