I am happy to recommend the following vendors:
Candice Giordano - G & G Horse Training
http://www.gnghorsetraining.com/
Candice is an excellent riding instructor, knowledgeable and patient.
Brown's Ranch & Supplies
20300 Almaden Rd, San Jose, CA 95120 (408) 268-4980
Brown's has a large selection of helmets, tack, and horse supplies at very reasonable prices.