Have you tried checking out Rustan's and S&R? Normally they have those rare products that are not usually present in some local groceries like Savemore, Puregold, or Robinsons. I remember my friend mentioned last time that she found a wide variety of steel cut oats in Market! Market!.
I found some steel cut oats before in Robinsons supermarket, you can find them in S&R as well.
Healthy Options! There's one in Greenbelt 5 :)