Sandy Celebration Crate

The call board next to Alyx will have a new Sandy Ransom Note

1. 
   
2. Go to Rustmaul Dig Site by the Shimmering Flats in Thousand Needles from Caverns of Time
3. 
   
4. /way #64 66.3 86.2 Rustmaul Dig Site Entrance is underwater
5. 
   
6. You must loot Water-Resistant Receipt here /way #64 64.9 84.4 Water-Resistant Receipt
7. 
   
8. Find Vashti the Wandering Merchant who patrols around the eastern road in Azsuna
9. 
   
10. Merchant will sell you the celebration crate with the Water-Resistant Recipe in hands for 500 gold
11. 
    

Note: I found merchant here but if you don't, open the NPC page to find his route /way Azsuna 66.21 47.65

Pick up Sandy Ransom Note on the billboard next to Alyx in Tanaris.

Go to /way 66.43 86.11. in Thousand Needles for the underwater cave entrance

Enter the cave and use your Idol of Ohn'ahra to find the Water-Resistant Receipt on the ground at /way 64.92 84.40,

Then take this to Vashti the Wandering Merchant in Azsuna (Broken Isles) who wanders up and down the road between /way 66.0 22.2. and /way 65.8 48.2.

Buy the Sandy Celebration Crate for 500G, accept the quest Sandy Celebration Crate and simply take it back to Alyx in Tanaris.

World of Warcraft has moved Alyx, the NPC in charge of the Guest Relation mystery questlines from the 20th anniversary celebration, to Dornogal, where they still accept missing Celebration Crates. She is just to the west of Stoneshapers Atrium next to the pool of water.