Any platinum ore nodes I find, I will post a screenshot and rough (very rough) directions as necessary. There are likely other precious metals near these locations as well, but I am specifically pointing out the platinum. Feel free to contribute.
In the nook where the Node Manager resides. 2 Platinum nodes.
On the mini-map, go right on the top road branch. You will find a cave that is dark as fuck. Go there, drop down when you come to an overhang with water at the bottom. Platinum is at the end of the water in the corner. 2 Platinum nodes. (It is noteworthy that this entire underground ruin has at least 2 of Sapphire, Topaz, Emerald, Ruby, and Diamond somewhere within.)
At the exact mini-map location. The giant moss-covered slab has a nook behind it. 2 Platinum nodes.
Follow the river beside Behr village west to its terminus. That shit is hidden in the shrubbery where the water stops. 2 Platinum nodes.
Northeast of Phoenil's Cabin. The hill will give way to an egress and a pond. A Mutant Tree Spirit roams nearby. 2 Platinum nodes.