The California Native Plant Society is a terrific resource. Many local chapters have plant sales.
www.cnps.org
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Las Pilitas Nursery has two locations, one in Escondido and one in Santa Margarita.
http://www.laspilitas.comThe Theodore Payne foundation in Sun Valley
http://www.theodorepayne.org/Tree of Life Nursery in San Juan Capistrano
http://www.californianativeplants.comThe Santa Barbara Botanic Gardens
www.sbbg.org
Yerba Buena Nursery in Woodside
http://www.yerbabuenanursery.com/Intermountain Nursery in Prather
Floral Native Nursery in Chico
www.floralnativenursery.com/
Mostly Natives Nursery in Tomales
http://www.mostlynatives.com/US Berkeley Botanic Garden in Berkeley
botanicalgarden.berkeley.edu/
Annie's Annuals in Richmond
www.anniesannuals.com/
Wyntour Gardens in Redding
wyntourgardens.com
Berkeley Horticultural Nursery in Berkeley
www.berkeleyhort.com
Cornflower Farms in Elk Grove
www.cornflowerfarms.com
Elkhorn Native Plant Nursery in Soquel
www.elkhornnursery.com
Forestfarm in Williams, Oregon
www.forestfarm.com
Freshwater Farms in Eureka
www.freshwaterfarms.com
Larner Seeds in Bolinas
www.larnerseeds.com
Siskiyou Rare Plant Nursery in Talent, Oregon
www.siskiyourareplantnursery.com
UC Davis Arboretum
http://arboretum.ucdavis.edu San Francisco Botanical Garden
www.sfbotanicalgarden.org
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Two mail-order sites outside California are American Meadows
http://www.americanmeadows.comand High Country Gardens
www.highcountrygardens.com
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Finally, I have to plug my friend's native plant landscaping business. The website is not quite there yet. He's in San Diego.
http://www.avibrantearth.com/--------------------------
Does anyone else have other sources for xeric plants?