You have to donate all fossils to the museum and if you have the 2nd floor shop in the museum it will be there the next day or the following. If it's not there in 2 days just keep going back every day. This is the same to get all the golden tools but the watering can. You have to buy 100 saplings, bushes, flowers, etc. Then talk to Leif and he will give you the watering can the next day.