You seem to have two options.
Buy the current material, the 642 exams are quite new anyway, and keep an eye open for announcements of changes. Take the exam before it becomes unavailable.
or
Wait to see if a new exam comes along. If one does wait until the old exam in no longer available, try to buy books for the new one, discover that they will not be available until after your expiry date. Buy whole set of new books and take all of the exams again.
Sorry if this comes accross as somewhat cynical. c'est la vie.
You may of course feel that some of the material has not changed much and you do not need to get all of the books.