You'll find several varieties of gochujang at East Asian grocery stores, or you can buy gochujang online (affiliate link). . Whole Foods sells gochujang and I believe Albertsons/Vons also sell gochujang. Store leftover gochujang in the fridge (it should last 2 years if sealed well). Same goes for gochugaru: East Asian grocery stores or you can buy gochugaru online (affiliate link). Whole Foods sells gochugaru, and the spice brand McCormick also sells it, though it's pricy for a small amount.