This is probably late in the game, but check these:
http://www.redlion.net/Products/Groups/SensingGears/SensingGears/Docs/11003.pdf
Redlion makes several gear sets to bolt on for this application. They are not the only supplier, but they do have several to chose from.
Good Luck!
If this is a limited installation, I would highly reccomend that you check with sick to see if they already have the interface you need. I know Keyence does. Most have a soloution that you can train to scan for specific barcodes and give a discrete or dry contact output.
This would...
Try these:
http://www.bannerengineering.com/products/photoelectrics/color_mark.php
Banner is a solid company, and I've used these in successfuly before. Zedder's right as well. Consistant lighting is the key to this project, but most of these sensors have their own light source to mitigate...
