u can get jambolon from any mattress/carpet wala shop. its not that hard to find. however it wont help in reducing the rattles by a considerable margin (it does but to a very small extent). what it will do is increase the output of the midbass (if done properly). u need to install dampening sheets to get rid of the vibrations. also take off the door panels and check all the screws and bolts. cut small pieces of jambolon foam and put it in places where the rattling may be coming from (eg the steel pin rods of the handles and lock across the steel plate or where the 2 metal plates are joint).
once ur sure you have done everything to stop the rattling caused by the components (im not refering to the component speakers mind that), u may cover the large/small holes in the doors. this will reduce the rattling from the door components and help with the midbass, but it wont do alot to stop the vibrations caused by the door plates flexing.