I have long purchased my vitamins from Koshervitamins.com . Today when I went to re-order I decided to look up 'Gluten free', thinking it would take me to all the vitamins they have that are gluten free, but instead , Surprise! It took me to 4 pages of GF foods.
So if you aren't able to get these at your market, when you are getting you GF kosher vitamins, order some of these products.
Just go to KosherVitamins.com and in the search filed type Gluten free. You will get a listing of 37 items they carry, which one of them is uncontaminated oat flour! So you don't have to make your own come next Pasach!