One sold 10 min ago, lets see if you can find it or not.

https://backpack.tf/item/7077625373 - Gambling, usable sales should be included.

Sale 1: Untrace/QS.

https://backpack.tf/profiles/76561198076494034#!/compare/1551225600/1551657600

https://backpack.tf/profiles/76561198289528232#!/compare/1544918400/1552003200

Sale 2: Untrace.

https://backpack.tf/profiles/76561198016663834#!/compare/1554076800/1554595200

https://backpack.tf/profiles/76561198446046760#!/compare/1554508800/1554595200

Sale 3: Untrace.

https://backpack.tf/profiles/76561198446046760#!/compare/1554595200/1554681600

https://backpack.tf/profiles/76561198267189538#!/compare/1554508800/1554595200

Sale 4: Transfer?

https://backpack.tf/profiles/76561198267189538#!/compare/1556668800/1556755200

https://backpack.tf/profiles/76561198449785042#!/compare/1528761600/1556755200

Sale 5: Use There.

Sold For Kill-a-Watt Milkman + 3 Keys.

https://backpack.tf/profiles/76561198449785042#!/compare/1556841600/1556928000

https://backpack.tf/profiles/76561198320964594#!/compare/1556841600/1556928000

Sale 6: Untrace.

https://backpack.tf/profiles/76561198320964594#!/compare/1556928000/1557014400

https://backpack.tf/profiles/76561198337734785#!/compare/1556928000/1557014400

Sale 7: ~17 Keys Pure.

https://backpack.tf/profiles/76561198337734785#!/compare/1557619200/1557705600

https://backpack.tf/profiles/76561198134873077#!/compare/1557619200/1557705600

Sale 8: ~20 Keys.

Sold For Blizzardy Storm Soldered Sensei (20)

https://backpack.tf/profiles/76561198109898906#!/compare/1553817600/1553904000

https://backpack.tf/profiles/76561198310972287#!/compare/1553731200/1553904000

Sale 9: Use There.

Sold For Cloud 9 Honcho's Headgear + 3 Keys.

https://backpack.tf/profiles/76561198310972287#!/compare/1553731200/1553904000

https://backpack.tf/profiles/76561198283662274#!/compare/1553731200/1553904000

Sale 10: Untrace.

https://backpack.tf/profiles/76561198283662274#!/compare/1554508800/1554595200

https://backpack.tf/profiles/76561198213234076#!/compare/1554163200/1554595200

Sale 11: ~16 Keys.

https://backpack.tf/profiles/76561198213234076#!/compare/1554595200/1554681600

https://backpack.tf/profiles/76561198331420429#!/compare/1554595200/1554681600

Sale 12: ~18 Keys.

Sold For Orbiting Fire Furious Fukaamigasa + Fountain of Delight Taunt: Yeti Smash + Strange Specialized Killstreak Crusader's Crossbow (1)

(B/O Cap 18, https://bot.tf/stats/listings/4PJV2G04)

https://backpack.tf/profiles/76561198331420429#!/compare/1554940800/1555027200

https://backpack.tf/profiles/76561198127540887#!/compare/1554768000/1555027200

Sale 13: Bulkish.

https://backpack.tf/profiles/76561198127540887#!/compare/1555459200/1555545600

https://backpack.tf/profiles/76561198002757046#!/compare/1555459200/1555545600

Sale 14: ~17 Keys Pure.

https://backpack.tf/profiles/76561198002757046#!/compare/1557878400/1557964800

Marketplace.tf Sales:

https://marketplace.tf/items/306;5;u19

Sale 14: ~19 Keys.

Mar 8

$33.85 / $1.8 = 18.81 keys

Sale 15: ~19 Keys.

Mar 24

$34.20 / $1.8 = 19.00 keys

Sales: 16/17/17/18/19/19/20

Going With 17-20 Keys.

Thanks to scourge for the premium, and shuffle for the help!