Marketplace Sales:

https://marketplace.tf/items/tf2/30332;5;u60

$22.22, May 25th

$22.22, May 26th

$23.95, June 2nd

http://manic.tf/keyprice?at=2020-05-25&price=22.22 - $22.22 / $1.88 = 11.82 keys

http://manic.tf/keyprice?at=2020-05-26&price=22.22 - $22.22 / $1.93 = 11.51 keys

http://manic.tf/keyprice?at=2020-06-02&price=23.95 - $23.95 / $1.94 = 12.35 keys

https://backpack.tf/item/2684262457 - Either May 25th or 26th

https://backpack.tf/item/7669706784 - same as above

https://backpack.tf/item/2532933407 - June 2nd

Other Sales:

https://backpack.tf/item/7669706784 (#1-4)

https://backpack.tf/item/2532933407 (#5)

#1

Untraceable

https://backpack.tf/profiles/76561198850274253#!/compare/1594166400/1594252800

https://backpack.tf/profiles/76561198129621897#!/compare/1573257600/1594512000

#2

Untraceable

https://backpack.tf/profiles/76561198129621897#!/compare/1594512000/1596412800

https://backpack.tf/profiles/76561198850121720#!/compare/1594512000/1596412800

#3

Untraceable

https://backpack.tf/profiles/76561198850121720#!/compare/1595980800/1596153600

https://backpack.tf/profiles/76561198340434037#!/compare/1594512000/1596153600

#4

Untraceable

https://backpack.tf/profiles/76561198340434037#!/compare/1596153600/1596240000

https://backpack.tf/profiles/76561198355651508#!/compare/1596240000/1596412800

Probably gambled

#5

Untraceable

https://backpack.tf/profiles/76561198432461884#!/compare/1590278400/1590451200

https://backpack.tf/profiles/76561198363395191#!/compare/1590364800/1590537600

Buyer re-sold on marketplace

#6

Untraceable

https://backpack.tf/profiles/76561198078018027#!/compare/1590969600/1591056000

https://backpack.tf/profiles/76561198180913187#!/compare/1590969600/1591056000

Probably gambled

Sellers:

https://i.imgur.com/JMqnX5O.png

https://backpack.tf/item/2684262457 - 10 keys

https://backpack.tf/item/5619856016 - 19 keys

https://backpack.tf/item/7957036181 - 19 keys

Sales at:

12 (3x)

Going to exclude the 10 key seller for now, considering you need to add them or visit their site to trade with them. Judging by the history, it looks like they may have only somewhat recently obtained the item, given how new the item ID looks.

Taking 12 flat.