Funny, they look chrome, not black, on my monitor...
They do look a bit too corroded to clean up nicely.
I've used the DEI brand from the local parts store, but it'll probably take at least 2 packages to do your deal.
You might try Speedway, Summit, or Jeg's.
You'll probably still have to blast or sand the flange areas and collector flanges & paint them if they're ratty.
Good time to make certain the sealing surface is dead flat.
I also like to cut away the bridge between the ports to eliminate warpage, improve access, and IMO improve the look.