Buyers: (Lowest c/o)

http://www.tf2outpost.com/trade/6719910 (16 key)

http://www.tf2outpost.com/trade/6721187 (14 key 1 ref)

http://www.tf2outpost.com/trade/6258892 (13 keys)

Sellers: (highest c/o)

http://www.tf2outpost.com/trade/6678123 (11 keys items)

http://www.tf2outpost.com/trade/6680542 (14 keys items)

http://www.tf2outpost.com/trade/6652420 (17 keys)

http://www.tf2outpost.com/trade/6257684 (add for steam noir)

TF2WH (Overstocked: 16 keys buy, 17.2 keys sell): http://www.tf2wh.com/item.php?id=928;6;6e54cac1ce077045c59ff73ae22382d3

Tf2tp sellers:

http://www.tf2tp.com/trade.php?trade=8737739 (b/o 18 keys)

http://www.tf2tp.com/trade.php?trade=8730806 (b/o 17 keys? Name: "P2 Soundtrack Boxes 17 Keys")

No one on outpost wants to sell for less than 18-20 keys, though you can find a few quicksellers. ( http://www.tf2outpost.com/trade/6741789 )

Waiting input from other mods.