There really is no easy road to the altissimo range, per se. While you may have a certain amount of luck with the “finger the note and blow” method, this is by no way a reliable (or musical!) means of accessing the register. Altissimo is produced not only by altering the length of the instrument (or, fingering the note) but also through the manipulation of the air stream and oral cavity, and through hearing the pitch in your head before you play. That being said, it is important to gain some proficiency with the overtone series before attempting to play in the extended range of the saxophone.

I would suggest the following resources:

“Top Tones for the Saxophone” by Sigurd Rascher
Published by Carl Fischer

“The Altissimo Primer” by Paul Cohen
Published by To the Fore