There is an article
here, by Tomba.
There is always the
How's stuff works site if you are into general knowledge about radiators.
If you are into radiator manufacturing, then you can try
ThomasNet for manufacturers.
All I can tell you is that old, room radiators, were made of cast iron, because is rust resistant. Modern ones are made of steel with low carbon content for the same reasons. Car's radiators are made of copper sheets, rolled into tubes with flanges left, or aluminium (I think the copper ones are better, because it has better heat conductivity).