3Rivers Archery has the "pencil sharpner" thing but it doesn't conver square to round. Do a search for "taper tool." The image won't show for the search, but just click on the "3Rivers Accurate Taper Tool $7.95" It's what tapers the ends of the shaft for points and nocks.
If you are talking about a dowel maker, then Lee Valley has them. "Veritas® Dowel and Tenon Cutters".
John