Just for clarity: You have not lost access to "maemo" on your phone, because what runs your phone is maemo.

I assume you haven't uninstalled anything and either you're talking about a shortcut on your desktop (not really a widget) to the maemo application installer (not HAM or FapMan), or you're looking for the OVI thingy that comes with a fresh install.

Either way, make a long finger press on an empty desktop space, choose Add shortcut from the Desktop menu in the top and add the lost shortcut. Presto.