Hello

I can't use all blocks. How can i do to make these available?

What do you mean by "all blocks"?

similar thing with myself, if an author uploads a map using some 'custom blocks' , if i don't have those blocks already in my game folder then i can't race the map.. Is there a complete download location anywhere to get all the available stadium custom pieces?

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