I have some very large heatsinks for sale - see photo. They measure approx 32 x 30cm and the longest fins are 7cm long. They weigh 5.5kg each. I do not have a dissipation rating for them but you would have to be building a truly monstrous class A amp for these to be inadequate!
They also look really cool
because of the curved profile of the fins. Price is £45 for one or £80 for two plus carriage. I have several pairs for sale.
They also look really cool