Hi, you can find it at any health store....I bought (Wild Oregano) OreganumPlus 1:1 made by St. Francis Herb Farm. It has Vitamin D3 in the Oregano Oil. Please don't use it by itself...it burns. I found that mixing it with water is a lot better than mixing it with honey. Tell your son it sip it as it tends to burn a litle. Don't gulp it down. I am 110 llbs and I use 5 drops, 3 times a day.
Good luck, I hope it helps.
p.s. I am not sure where you live but I live in Toronto and can get it from any health store