2 sales

1) $38.88 on January 23rd, keys were $1.75

https://marketplace.tf/items/1107;5;u3015

38.88/1.75 ≈ 22 keys

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------

2) 23 keys

https://backpack.tf/profiles/76561198026707500#!/compare/1546128000/1546214400

https://backpack.tf/profiles/76561198308261655#!/compare/1546041600/1546214400

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Total: 22, 23

If you will find other sales, you're welcome to report them.