Amateur box maker, Dr. Nestor Demianczuk, asked about the availability of tapered sanding disks like I have used in my early books, Creating Beautiful Boxes with Inlay Techniques and Simply Beautiful Boxes. He has used flat blades for the purpose but found that they tend to cause friction burns on the stock as the sandpaper loads up.
My original tapered sanding disk came from Sears, but as far as I know they are no longer available. I have also used a flat blade successfully by moving it over to engage the wood in gradual increments. As Dr. Demianczuk has noted, if you try to take off very much at once, the leading edge of the disk loads up quickly and can make friction burns on the stock, so the trick is to lighten the load, taking smaller increments. A tapered blade would be very easy for a manufacturer to make, and a flat sanding blade could be adapted to a slight taper very easily by a modern machine shop. Hopefully, some enterprising manufacturer will again make tapered sanding blades, as they can be useful to box makers. In the meantime, flat sanding blades are offered by Woodcraft.com