Exactly what limit are you talking about? Pleae explain. The only limit that I am aware of it the limit of the records returned by the record source for the combo box.
The ROW SOURCE has a maximum of returning 65,535 rows. If you need more than you will likely have to use a combination of controls, either combos or textbox with combo to first cut it down a bit so it will fit.
Also, when you do have so many in the combo, it isn't necessarily going to be able to scroll to them. You can start typing to get the first few characters, and then do the drop down.