Here is the Headless Horseman's sales history in Roblox: October 31, 2013 - November 3, 2013 October 10, 2014 - October 30, 2014 October 1, 2015 - November 3, 2015 October 1, 2016 - October 31 ...

If trading for the Headless Head isn't possible, Roblox players will need to wait for it to go on sale in October. For 31,000 Robux, it can be bought with the Headless Horseman bundle.