Are there any weapons that have the heavy property, but not the Two-handed property? I am looking for something that my Bladesinger wizard can use Great Weapon master with.
A brief survey of the equipment tables found in chapter 5 of the Player’s Handbook shows no mundane weapons which have the heavy property but lack the two handed property. This observation is confirmed in the Sage Advice Compendium in a question about the Dual Wielder feat:
Every heavy weapon in the Player’s Handbook also has the two-handed property.
Further, there are no magic items that fit either, though a more thorough investigation is required to independently verify this.
And this makes sense. The reason two handed weapons require two hands is typically their weight (though the double bladed scimitar is an exception). We should expect any weapon heavy enough to get the heavy property to be heavy enough to require two hands. It also makes sense from a balance perspective - as Tiger Guy pointed out in a comment, a one-handed heavy weapon would allow the use of GWM with a shield, which would be an exceptionally strong combo.