Hi dip,
There aren’t any local factory direct manufacturers near you but there are a couple of possibilities in terms of local retail stores. These will need more research to find out how knowledgeable and open they are about the materials in their mattresses. I’ve also listed the brands that they carry that may have better quality/value.
http://www.couchpotatoslo.com/ San Luis Obispo. Diamond
http://www.onlinemattressoutlet.com/ San Luis Obispo. Arroyo Grande, Atascadero. Stress-O-Pedic, Therapedic
http://themattressstoreandfurnituregallery.com/ San Luis Obispo, Grover Beach. Diamond, Paramount.
http://www.shoprandr.com/ Arroyo Grande. They carry some major brands which I would avoid but they also carry Pure Talalay Bliss latex mattresses and Diamond mattresses which may be worth considering.
http://www.harringtonhomefurniture.com/mattresses/2 Atascadero. Diamond. Be very cautious here to make sure that any mattress you purchase is new AND has a factory warranty and isn’t what they call an “overstock” or a “scratch & dent” or "blemish (which are usually used or returned mattresses).
http://santamariatimes.com/places/furniture-depot/business_4000001018.html Santa Maria. Golden (they may have some good value memory foam), Diamond, Gateway, Stress-O-Pedic
http://weatherbysfurniture.com/ Santa Maria. Stress-O-Pedic
http://www.stylehousefurnishings.com/home.html Atascadero, Nipomo. Stress-O-Pedic
The closest Factory direct manufacturers to you that I’m aware of would be in the Santa Barbara/Ventura list in post #2 here or in the Monterey/Salinas/Santa Cruz/San Jose list in post #2 here or in the Fresno/Visalia list in post #2 here.
Hope this helps.
Phoenix