I decided to keep track of my smithing statistics, if anyone is interested you can see it here.
The lines colored indicates rare swords. Unfortunately Touken Ranbu Helper didn't record everything properly, so the rare swords I still remember the recipe but TKH didn't record I put in the end. I'll try to update this page frequently.
As you can see most of my rare swords came from smithing as I have no luck with grinding... I'm still looking for Kogi in map 5-3, but if someone has a good recipe for him please tell me!!