Currently Being ModeratedFeb 22, 2013 8:42 PM (in response to mgounder)
Take your AirPort Express down to a nearby Radio Shack store to see if one of the AC power cords that they normally stock will fit. It will likely be black....not white....but you will likely find a matching cord that will work.
Currently Being ModeratedSep 9, 2013 8:21 PM (in response to mgounder)
I'm sure the OP found his solution, but I wanted to share mine in case it helps some future seeker.
There are a lot of brand new cords on eBay for less than $10 including shipping, which is way cheaper than the $39 stereo connector kit or an AC adapter from a retailer. I just bought a used-like-new one for $5.50.
The cord is made by Volex, part number APC7Q. The Apple part number is M9573LL/A. If the seller got it from the stereo adapter kit, they'll probably list it under MD836LL/A, which is the kit's part number. I got the best search results on eBay using just the Volex part number.
Best of luck!