Well hey...if I came across as a little too snotty, I apologize.
Emery cloth, crocus cloth, or 400-grit sandpaper should all do the job, and should be available at any Ace hardware, Lowe's or Home Despot. If you've got some Brasso or Flitz metal polish at home, it should work also, but it'll take longer than the sandpaper would. You may want to come in with the liquid metal polish after the harsher abrasives to really "shine-n-fine" things up. I'd also suggest trying out your polishing medium on the left-hand side of the chamber block/hood area first, so that any unsightly blemishes will basically be hidden by the slide instead of being visible through the ejection port. Normally, I'd also suggest wrapping the abrasive cloth/paper around a sanding block to keep from dishing/rounding the surface, but since the Melonite treatment is supposed to make the barrel surface almost as hard as diamond, the sanding block may not be necessary.
If you like the results you get, and it saves you having to buy a $200 aftermarket barrel of undetermined reliability, so much the better...