I've never seen Sünner, but I can get Gaffel. I prefer it to Reissdorf, but it seemed to be in better condition too.
Drinking bottled Koelsch is like eating canned peas. It can be decent, but it's not nearly as good as fresh from the brewery/garden.
A well-made, absolutely brewery-fresh draught Koelsch is amazing. There are loads of delicate, tongue-teasing fruity esters (apple, pear, fresh cherry), subtle floral noble hop aromas and flavors and a subtle vinous finish, combined with a slight creaminess and effervescence in the mouthfeel. Bottling Koelsch somehow reduces the delicate yeast and hop notes. Letting Koelsch age for any length of time also kills it, turning it into nothing more than a vaguely funky Blonde Ale.
My experience is that most imported Koelsch isn't worth drinking. Even if it's treated well, unless it's kept very cold, it's lost a lot of character by the time it gets to shelves in the U.S. Also, retailers generally don't understand the style so they keep it around long after its "best by" date. There's nothing sadder than going into your local bottle shop and seeing bottles of Gaffel or Reisdorf with a thick layer of dust on their shoulders.
Even American-brewed Koelsch-style beers can lose a lot, especially if they've been pasteurized or heavily filtered. Since many are summer seasonals, they might also sit around in warehouses which are just a bit too warm on their way to the consumer.
Is that if you can't get to Cologne, your second best strategy is to find a good beer bar which has a well-made, fresh, domestically-brewed Koelsch on draught.
On the East Coast, you should be able to get Harpoon Summer Beer and possibly Capitol City Capitol Kölsch and/or Goose Island Summertime. I haven't had it, but apparently Gordon Biersch Sommerbrau is also good.