Never tried it on a combobox, but couldn't hurt to try (this works on text boxes).
First you have to create a custom shortcut menu on which you place the find command (normally part of the Edit menu bar).
From Access help (primarily):
This can be brought up by entering "shortcut menus" in the help wizard, then selecting "working with menu bars and shortcut menus".
On the View menu, point to Toolbars, and then click Customize.
On the Toolbars tab, click New.
In the Toolbar Name box, type the name you want, and then click OK.
On the Toolbars tab, click Properties.
In the Type list, click Popup.
Set the AllowCustomizing property the way you want, and then click Close.
Microsoft Access adds the shortcut menu to the Shortcut Menus toolbar, from which you customize all shortcut menus.
In the Toolbars box on the Toolbars tab, click Shortcut Menus.
On the Shortcut Menus toolbar (this now appears towards the top of the window), click the Custom category.
Select the custom menu you created.
Move or copy commands from other menus.
If you have questions go into help as instucted above, as it also gives a few explanatory links.
Next you must go into your form's properties and set Shortcut menu to YES, then click to the right of the box under Shortcut Menu Bar and from the dropdown box select the custom menu you created. This is now your shortcut menu for the form.
If you right click on the control you want to search (at least if the control is a text box) this selects the object as the field to search, and ther you go.
I hope I haven't forgotten anything (if I have I'm sure someone will jump in) and that this helps.
The Missinglinq