we've substituted plain zinc oxide before and it worked but it was only 20%. I don't know if that's across the board or what...but anyway even if so, that's better than 10%, right?
However, about the Desitin. You won't find the 40% Desitin in the infants department of Wal-Mart.
It's sold in a large tub, with a purple lid, it's about $13, and is in the Health and Beauty section of Wal-Mart in the "baby needs" aisle. I don't know why it's not in infants, but it's not!