Jul 13, 2005 - AutoComplete ComboBox
Using a Macromedia Flex ComboBox Control with autocomplete

An unofficial solution that may or may not work from someone who's name may or may not be Matt. :)

 Unfortunately this is something you’ll have to build yourself.  If I were inclined to look for some undocumented support I might remember that the ComboBox dropdown is a List which is a subclass of ScrollSelectList.  I then might consider using one of those undocumented techniques to view the source of ScrollSelectList and looking for a function that might help me out, something with a name starting with “find” for example.