I don't know where to find that exact punch.
An alternate method to mark the center of a dowel would be to drill a ½ inch hole in a chunk of wood (face of a 2x4 perhaps), insert dowel part way through the hole, and use a ½ inch transfer punch to dimple the center of the dowel end.
Online search can find you a set of transfer punches for a bit over $10.
HTH.