Are they found by progressing more of the story? Or are they special loot items, or are they by getting things to open up in the bazaar or found in shops as you progress?

I just would like to try and get something really awesome, for awhile now some of my top weapons are like Icebrand and the Yoichi Bow, just would love to find a killer sword or a sword i could do a sidequest for perhaps...just not sure if there is any.