User blog comment:Plexioth- xD/Monster Hunter 3 Ultimate/@comment-3095304-20130321021736/@comment-4933023-20130321022440

They're pretty uncommon. The nodes in the tundra have a ten percent chance for lightcrystals. The rate goes down with high rank to eight percent.

So a harvest tour of the tundra is where I got mine. Look for blue nodes.