You can find this flying fish roe in Asian grocery stores, sold in many colors. It’s fermented in a sweet and salty marinade that also includes MSG, so I usually wash it in running water and freshen it up with some lemon before using it.
My cookbooks
Which to get? my first book has all the recipes for all the essential Korean pastes and sauces, but my second book Maangchi's Big Book of Korean Cooking has more recipes. Both are best sellers and either one is a good choice if you want to learn Korean home cooking.