After being reminded that these strings are unused, yet supposedly appear tarnished, something didn't sound right. Not being a materials expert, I did a quick google, and found the following statement in WikiPedia:
On account of its permanence in air and inertness to oxidation...
(link) While WikiPedia has taken some flack recently for a few deliberately misleading entries, I also read that a recent study showed them to be slightly more accurate than Encyclopedia Britannica (though based on a very small sample). As with anything you read, use your own judgement.
I would suggest that the term pure nickel, used for marketing purposes on strings, is not quite as tightly regulated as some of the wording we see on food packaging these days. Some are more pure than others, and if they have truly tarnished/oxidized, then they aren't.
Even so, as long as they are unused, I would start by simply wiping them down with alcohol or something, before resorting to more drastic measures. Maybe what you're seeing is residual manufacturing oil or something. And since you paid only about $1 per string, I would personally just throw out the ones that sound bad to start with (especially since it's your dollar...).
Oh, and I think I'll continue to broil my salmon, at least until I get a new dishwasher (I hear those Miele's are pretty sophisticated).
-Bob