1/2" or 3/4" thick beveled wood segments glued up around a cylinder, then rounded on the outside with my 12x36 metal working lathe (due to lack of a wood lathe) is another possibility. Doesn't especially need to be concave on the inside. Tedious work, but it may end up being the way I do it. Wood thickness depends on the arc that is close to what a cookie filling scaled to 10.5" would look like.
I have done many fiberglass lay-ups on molds for UAV, RPV, and wind tunnel models in the past. You wouldn't know it is fiberglass when the guitar is completed. In that case, I would machine a plug mold on the lathe as the core for the fiberglass part that I need. The fiberglass part would be lighter than a segmented wood ring.