Hmm, that is a large chunk of firepower.
Well, they have a 14 second reload time, so you can burn the initial salvo with 450 cheap ships (Neinzul would be good here).
Then it's a matter of getting something pretty fast with a good bonus against them. Acid Sprayers are an obvious choice if you have them (100x bonus). Autocannon minipods get an 8x bonus so as long as the swarm lasts they'll be pretty good with the cluster bonus (some cloaked raids could be effective too). Deflector drones get 20x against them. Armor gets 10x. Youngling weasels get 20x. Even ordinary bombers get 16x. Raiders get 12x. Tanks get 40x.
Obviously your mileage with the various bonus ship types will vary based on whether you have them, but I imagine worst to worst you could use a bunch of fighters to draw the first salvo, and send transports full of bombers to unload right on top of the bombards (though the slow unload rate will hurt, may want Transport IIs for that).