The problem with a combo box is that most of the properties, including OnClick, refer to the combobox more than the textbox associated with it. To do it you'd have to lay a text box on top of the combo box just short enough to allow the drop down to be clicked and have the value be the same. This has it's own problems as well such as autocomplete when typing in won't work.
It sounds more like you want to type in a date in a text box and have it look up similar to how a drop down can be coded to work.
You CAN do this with a text box control. It has an OnChange routine in which you can code your own lookup procedure. Or you could have a button next to it, use the eyeglass icon if you like, which will perform a lookup based on the date put in the text box. Then use Me.Recordset.findfirst("Where TheDate = "#" & My_TextBox.Value "#").
Does this give you pointers in the right direction? If not, or you're not comfortable with coding custom routines, I'd need more details on what you want.