Where can you find a key to Wyvern Hill in Pokemon mystery dungeon blue rescue team?

The key to unlock HM Fly in Pokemon Red Rescue Team can be found in the Dream Maze by completing the task given by the Kecleon Shopkeeper. To obtain the key you must bring the Kecleon Shopkeeper the following items:

• Lost Item: Big Mushroom
• Lost Item: Tiny Mushroom
• Lost Item: Pretty Wing

Once you have the items go back to the Kecleon Shopkeeper and trade the items for the HM Fly key. This key will unlock HM Fly allowing you to use the move in battle or to open up new areas of the game.