Some print shops will make pads in any size. If you only use the front of each page, they can use their scrap paper from misprinted runs. Once you tell them the lenght and width (and weight) of the paper in the pad that you want they can put a gummed edge on it, probably any thickness you want within reason. Then you can just tear off a hunk the thickness (or use a razor blade to score the adhesive) you need for a refill. These must be cheap to make because I used to get scratch pads in all kinds of sizes for free from print shops.