aaah that you mean.
Sadly I have to say 'no'. There is no complete list of custom objects anywhere. You can find a lot of them on
http://www.maniapark.com/liste_object.php?game=1
But if there are maps that use custom objects and the map is not made in a titlepack and the custom objects are not embedded into the mapfile, then there is no chance in opening the map. Even if you add the custom blocks to your game folders.
I wish Nadeo handled this differently, but well... maybe there'll be changes in the future