Goldfish aren't fussy eaters and will east almost anything.  You can feed goldfish vegetables, pellets, flakes, and live food.
There are many commercial pellets and flakes available so that shouldn't be too hard to find.  As far as live food, you can feed goldfish Dalphnia (they're available in many sizes so choose the size that is best suited for your goldfish), Brine Shrimp, mosquito larvae, Tubiflex worms, meal worms, wax worms , blood worms. The live food is available at most reputable pet stores.

Goldfish are omnivores so they will eat almost anything. It is always good to vary the diet of your pet just as we humans like and require a varied diet in order to stay healthy.

You can offer your pet goldfish many different types of food. These can include flakes and pellets, frozen or freeze dried foods, household foods, and live foods.

Prepared commercial foods such as flakes contain the essential nutrients to keep the goldfish healthy and should be the main part of its diet. You can vary the diet by adding frozen or freeze dried foods, which have all the benefits of live foods but without the risks of passing harmful pathogens to your pet fish. Live foods can be risky because some can carry pathogens that can infect and kill your fish. Goldfish will enjoy household foods such as lobster, oysters, clams, canned vegetables (like beans) and fresh vegetables (spinach, brocolli).