The Latin Technique adopted by IDTA is Walter Laird's, and the Ballroom Technique is Guy Howard's. Neither book contains the current syllabus, but you could not make a serious study of the syllabus content for professional examinations without these texts.
The current syllabus is not published online, as far as I know, but in a slim volume called "Profesional and Amateur Dance Syllabus". The current syllabus was revised in 2006, and copies cost 8 GBP, direct from the IDTA shop, and it is also resold through third parties (usually for more).