Actually, there has been no specific text for the STPM course of Further Mathematics.
You would need to know the syllabus of the Further Mathematics course(probably available from your teacher OR just get it from MPM), then according to the requirements stated for each topic go and find out the information (maybe in your state library or school library).
There is an old book of Fajar Bakti on the FM but then it still does not cover every parts of the new syallbus yet , particularly on number theory and graph theory. These 2 topics are the new added ones.
You could also try to get the books pulished by Oxford on FM, which is quite informative and should have covered the Paper 1 of FM.
Hope that helps.