The History Extension Source Book of Readings is available from the BOS website, as a
PDF.
It has enough material to keep you going for a fair while. If you want to get overview texts like
History and the Historians by John Warren (a fairly mediocre book IMO, but one that most schools seem to use), you might have to buy them off Amazon or something, or get your local bookshop to order it in - most shops will do this for you.