You can get a new 30-11021 on eBay for $16.99 (plus shipping). So you get 4 replacement lights, plus 4 barricades, plus the controller! If this is the price point I'd be surprised to find "just" one light as a replaceable item.
An OGR search for 30-11021 for digging deeper essentially pulls up just this thread. So this being a discussion forum, if you want to discuss DIY options for the common good, I figure it should be possible to repair a broken light.
Couldn't find a better closeup photosof the light on the web but it looks like an amber LED inserted into a clear solid plastic "lens." The lens looks suspiciously like a slice of round acrylic rod flattened on the bottom.