Welcome to the forum.
Have you tried MB? As they still stock many many parts for the older vehicles, and i have found for similar parts very cheap for 202.
Failling that you could try the classic car magazines classified's as I have seen companies specialising in sound proofing for older vehicles, but i think MB will be the cheapest and best option.
Yes Mercedes Benz main dealer, IIRC the under bonnet insulation on a W124 is bonded to the underside of the bonnet, it would never come of in one piece thats why I never mentioned a second hand source.
Is yours just missing? if so you will probably see the remains of the bonding agent on the inside of the bonnet.
Thanks guys.For the record the hood pad has just disintegrated on one side so it will all have to come off.I running with halk of it at present and to be honest there is not a great deal of noise difference, around town anyway.