Sonali,
I don't know of any examples of a search textbox class, but it shouldn't be hard to build. Just us the Vaklue property in the Valid event to look up a match, if there is only one use it, if there is more than one call a form to have the user select from the group.
The real problem with lists and comboboxes is that they keep their entire list in memory. When the list grows too large then performance is hurt. Lists and comboboxes are really good when 1) the user doesn't mind using the mouse, 2) the list is short (50-200 items), and 3) the list won't grow very much over time.