Old growth means it's from a 150+ year old tree, regardless of grains per inch. I'm sure if your shaft is old growth, Mr. Downey would have made it very know. Old growth wood is not commercially cut so there is none for shafts to be made from. The only way is for the builder to either cut his own, or have a source. It is sometimes specialty cut by smaller production or personal mills, but it's stupid expensive & very rare. The easiest way to obtain it is to cut it yourself.
I'm sure your shaft is a great shaft coming from Mr. Downey. There's no need to pursue another simply because of grain count. Maybe that can be something you look for on your next cue.