Not sure if you still need it, but for anyone else who is having a hard time like myself, I found a whole bunch near the following coordinates:

73.2 - 77.5
78.1 - 75.4
80.8 - 76.4

It seems to spawn near the base of the cliffs in the desert biome. These were just the first batches that I've found, so I'm sure there's more if you know how to look for it! Good luck!