Add missing package source for external Components packages

build/sources.props

@@ -19,6 +19,7 @@
       https://dotnet.myget.org/F/aspnetcore-dev/api/v3/index.json;
       https://dotnet.myget.org/F/aspnetcore-tools/api/v3/index.json;
       https://dotnet.myget.org/F/aspnetcore-master/api/v3/index.json;
+      https://dotnet.myget.org/F/blazor-dev/api/v3/index.json;
       https://dotnet.myget.org/F/roslyn/api/v3/index.json;
       https://dotnet.myget.org/F/roslyn-tools/api/v3/index.json;
       https://vside.myget.org/F/vssdk/api/v3/index.json;