How to use/obtain a Chayenne key?

Question

Nowadays it can only be bougth in the market or it has some quest?

Answer 1

The only way to get it is buy it on market/other players. Because this was part of the celebration of 15 years anniversary of Tibia.

And the quest where you use it is: Chayenne's Realm Quest.

Answer 2

It cannot be be obtained as a loot or reward anymore in the game - you can only buy it from other players. 

Was a very rare loot from Chayenne's Anniversary Remains during Tibia's 15th Anniversary. CipSoft has held events which had this item as a reward. It's very valuable because of its exclusiveness and because a quest requires it. As a consequence of its rarity, the quest's exclusive reward is also very valuable. ‘ Required in the Realm of Dreams Quest.

Source Tibia Wiki

It was also gifted by Cipsoft during contest for Cheyenne story- organised in honour and as a farewell for her. Winner were: 

• The Music Box (untitled), submitted by Abiston
• The Last Draconian, submitted by Azurai
• Dragon Race (untitled), submitted by Jinxz

Answer 3

The only way to get it is buy it on market or with other players. This was part of the celebration of 15 years of Tibia and u cant obtain more.