From: 3.0 Patch Notes.
* Grade five materia for crafting and gathering classes will not be available at the release of patch 3.0. They are scheduled to be added at a later date. However, it will be possible to receive grade five crafting or gathering materia via materia transmutation by speaking with Mutamix.
I didn't see any mention of other methods of getting grade 5 materia from any patch notes so for right now, this is the only way.