I just got a phone call from Fastenal and they sell these but on a special order only basis. They aren't listed on the web site, you need to get in touch and have them brought in.
The good news is they are only $14.20Cdn each (about $10USD?) so it's a good savings over buying a whole new set at $54USD. I have yellows on my RAS but want to be able to feed from either end so I'll just change from yellow wheels to Orange wheels when necessary. At this price I may also order a set of greens.