You can go to the search page and type in Unknown in the make field. You can then sort them by date if you want to see the most recent first:

http://www.imcdb.org/vehicles.php?resultsStyle=asImages&sortBy=5&yearFrom=&yearTo=- &makeMatch=2&make=Unknown&modelMatch=1&model=&modelInclModel=on&modelInclChassis=- on&mk=&origin=&madein=&madefor=&role=