There isn't a ComboBox Object in EQ2 componet list
If one wasn't lazy like me they could make a getto one though.
Place a input object on top of a dropdown object but dont' use the full width of the dropdown, leave the handle sticking out. Now when the use Onclicks the handle of the dropdown make the input box !visible and when the user Onselsects or OnHoverOut make the input box visible and transfer the the selection to the input box.
Way to much work for me, but /shrug.