you can get 535 pieces at timeless isle, with
1. collect 50K timeless coins and buy the horn form vendor beside the panda king,
2. buy a treasure box key with 500 timeless coins, and try your luck, i had got a horn form the box,
3. do the group quest that will reword a horn, its hard to do .......
4. go top of the timeless isle and kill the boss inside raid may drop horn, but its not opened,
then use the horn on any UNUSED 496 armor pieces, it will give you a random stat 535 piece.
PS. the horn cant use on rings and relics.