Is there anyway for a player character to get the
Threatening Reach or equivalent ability with a reach weapon?
Apart for one-off's like artifacts such as the Spear of Urrok the Brave [ddi]
Pure threatening reach does not exist as an always on thing.
However, there are a number of close approximations.
From earliest level we get:
Spiked Chain Expert (Multiclass feat) 8th level Lets you swap out for Chain ward a daily power that gives you a threatening reach stance.