Classifieds as of the post of this suggestion:

x1 at 18 Keys - Gifted. ( http://i.imgur.com/voQl1DZ.png )

x1 at 18 Keys - Not gifted. ( http://i.imgur.com/lZxgawu.png )

Sellers:

http://www.tf2outpost.com/trade/19964669 - 1 Earbud (17 Keys) - 1 Sold - Still selling 1.

http://www.tf2outpost.com/trade/19917232 - 1 Earbud (17 keys) - 3 Days old - History on it is very weird - Either sold or being brokered.

http://www.tf2outpost.com/trade/19963617 - 1 Earbud + 4 Refined.

http://www.tf2outpost.com/trade/19966013 - 18 Keys.

http://www.tf2outpost.com/trade/19970709 - 18 Keys.

http://www.tf2outpost.com/trade/19959956 - 19 Keys - About 2 Days old - Reposted in trades.

http://www.tf2outpost.com/trade/17274894 - 19 Keys - 4 Months old - Autobumper.

Rest on market are either only for sale in sets, up for unusual offers/upgrading or 20 keys+.