If you have a temple, information on an Internet simulation of an ancient temple to Rhea, or sites devoted to her, please contact me at nanai_leshk [at] gmail [dot] com if you want it added to the list.
Information on worshipping the Hellenic Gods can be found across the Internet. Start with Theoi.com's page on the Great Mother and some basic nuts-and-bolts info on how to make offerings.