tnazaruk You will need to enable ca_object_representations in app.conf to have them show up in the Find and New menus. Most people don't want this, which is why it's disabled by default.
HOWEVER, you can seach for representations through objects, by entering the following into the basic search field
ca_object_representations.original_filename:the_filename_you_want
You can also add the filename accesspoint (assuming your system has this) into your object advanced search form.