My husband, 73, has been prescribed this vitamin supplement 2 x a day. We are having trouble finding them here, in Griffin, Ga. at Walmart, Walgreen s. CVS. Is there a problem with distribution? Can we substitute a store brand. We have compared some but find a few differences that I feel may be important. I am a registered nurse and want my husband to have exactly what he was advised to take by his cardiologist. Thank you.