Milk and milk products are good sources of riboflavin. Riboflavin is also found in whole grains.Riboflavin is one of four vitamins added to enriched grain products such as enriched flour and breakfast cereals.. The other vitamins added to enriched grains are thiamin, niacin, and folic acid.Figure 1.iboflavin is also found in whole grains.Riboflavin is one of four vitamins added to enriched grain products such as enriched flour and breakfast cereals.. The other vitamins added to enriched grains are thiamin, niacin, and folic acid. Figure 1.