"by inserting tracking tags in the saguaro's" A special scanner can be used to detect a tag inside a saguaro.
Tucson cactus and Succulent Society has a Crested Saguaro article on Crested Saguaro Society -
in the July-August 2007 issue of the Cactus & Succulent Journal.
Wallace Desert Gardens ranking among the world's largest collections of cacti and succulents- has several Crested saguaro's.