Why do you need actually System.Data.Linq? The one is needed to work with something like Entity Framework (MS SQL database, for instance). But you don't have those on your Android.
You'd rather work with something like SQLite
(ORM-way).
But in that case you need just common Linq to objects from System.Linq
namespace.
(You might also want to consider using MvvmCross framework (including, for easy access to Database (or any other specific functionality)). That framework would allow you to build all the data access logic separatly from your interface and support multiple platforms (iOS and Windows Phone as well)).