@RainGnyu I had to do constant cradle runs for about a week to get mine to finally drop so I know how you're feeling. I was running at a lower overall RDR back when I farmed mine though.
There's no secret to it. You just have to keep spamming cradle. The only other thing you can do is pray you get lots of PSEs. Every PSE you get is a real shot at getting it because of the sheer number of mobs dying. Every single mob in cradle has a chance to drop 15* stuff including the sword.
Wow cool I feel better now......on the real. Thanks!