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.
![30-11021 30-11021](https://ogrforum.ogaugerr.com/fileSendAction/fcType/0/fcOid/158111058908709853/filePointer/158111058943441072/fodoid/158111058943441069/imageType/MEDIUM/inlineImage/true/30-11021.jpg)
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.
![30-11021 light fixture 30-11021 light fixture](https://ogrforum.ogaugerr.com/fileSendAction/fcType/0/fcOid/158111058908709853/filePointer/158111058945771882/fodoid/158111058945771880/imageType/MEDIUM/inlineImage/true/30-11021%2520light%2520fixture.jpg)
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.