Compendium says they're limited time only but have been part of challenge requirements a few times now.
I want to say one of the dungeons has them because I have about 6 sets and I never remember intentionally grinding for them.
Summon the strength of millenniums past, forged by the fire and flame
I am the weapon of empires vast, Immortal is more than a name
MuzakMaker-3591
I will point out that the new talisman icons on the character info screen makes this sort of ting SOOOOOOOOOOOO much easier. No more back and forth to the team screen to verify what talismans are on what character
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CLANLESS
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All there is in this app is to spend money or collect yet more frags... entirely pointless and unfulfilling..
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I agree it's great, but will be even better when they get it working properly. Right now the talis icons don't display/refresh after just equipping talis in My Team of arena, gauntlet, etc. So now I'm constantly going back and forth anyways to confirm what talis I've just put on my team every time before I go into battle. Also, sometimes randomly the equipped talis Set Effects area doesn't display anything for some reason now.
Step in the right direction though. Hope they clean that up soon. Nice touch.