This is another style who's finer points can get lost in translation on the trip from Germany. Domestic examples are best (when done well).
If you're in CO, find a good Rock Bottom location. Several locations make a kolsch, most of which are well done. The Indy College Park location brews the best kolsch I've ever had. Foreign or domestic.
Do you get Schlafly in Colorado? They make a GREAT kolsch.
I haven't had the Gordon-Biersch kolsch, but there other offerings are pretty authentic. Worth a shot. Same goes for Victory.
Trader Joe's makes a fair example (Summer Brew), but freshness counts since they don't refrigerate. Its seasonal (I think), so pick one up when it first hits the shelf.
Rogue makes a honey kolsch that is quite nice. If you can segregate the honey character in your head, its a good example of the BJCP style.
Goose Island Summertime used to be a decent example, but I haven't had it since ABI started brewing it.
If you find yourself in the Indiana/Chicago area, Calumet Queen by 3Floyds is superb.
Reissdorf is widely available but is on the bitter end of the style IMO. I usually have it on draft, so the bottle version may be less bitter (but also more skunky/oxidized).