I don't have enough data to give hard numbers on this, but in my experience the level 55 left side gear (ramie/dhalmel) gives tier IV materia more often than it doesn't. Easily worth the NPC vendor prices for the gear especially if you meld junk materia to them to compensate for it being NQ.
There aren't a lot of great ways to blitz spiritbonding these in one sitting that haven't been mentioned above, but if you keep using them when you can then you'll get a decent supply of them over time. I'll just switch to the spiritbonding gear set whenever I need to make a bunch of refined mats that don't need to be HQ, for instance.
