Its just luck really. There are many drops from cronus and gladiator so chances are low, yet that said it should only take around 10-30 times. My best advice is to find a group who you feel confortable with, in the sence that you know you won't die. Also you might want to use a team tactic, maybe all blades one person. Or maybe you all hit but there is one healer. Or something like that its up to you. With a good team you can kill them in about around five miniutes depending on you tactic.
As BrynnerOfReign said no tricks. All drops by them are completely random. The Athame was easier for me to get at around 15 tries and the ring took me 30 tries. Mostly just luck Megan Frostflame Level 100 Child of Light and Shadow