San Pedro - FAQ on the potency of this mescaline-bearing cactus.
-- http://www.erowid.org/plants/cacti/cacti_sanpedro_potency_faq.shtml   Related: recreation;  

PsychedelicMushrooms.com - Carries an assortment of ethnobotanical and herbal products including Hawaiian and Mexican mushrooms, salvia divinorum, Ayahuasca preparations, San Pedro cactus and other psychedelic herbs.
-- http://www.psychedelicmushrooms.com   Shopping: Recreation: Drugs  

Plant Planet - Sells specialty cacti including San Pedro cactus. Also ceremonial incense, Peyote art, and miscellaneous merchandise.
-- http://plant-planet.net   Shopping: Home and Garden: Plants: Cacti and Succulents  

Herbal Fire Botanicals - Offers a selection of ethnobotanical and herbal products, including salvia divinorum, mushrooms, and San Pedro cactus. Products are mostly extracts and plant parts, with a few seeds also available.
-- http://www.herbalfire.com/   Shopping: Recreation: Drugs