Well, the concept art for WHM AF and the Thyrus doesn't include dimensions sadly, but it does show the weapon in size relation to it's wielder (artwork also exists of it being used by a lalafell WHM), so all you can really do is take that design and apply it to a real world item like a broom handle, and derive some dimensions from that. I dont think you'll ever be able to get the 'exact' dimensions for it though, as they pretty much don't exist. Anyway, good luck with your costume! I'd love to make my own WHM AF costume, but I just don't have the time sadly.