Ebay isn't considered a national retailer due to parts quickly going out of "stock" but since "a majority of teams" could purchase the slide components from
http://www.adafruit.com/ then you should be fine under R04. A real "nitpicky" inspector might argue that you all have bought an assembly rather than just a COST part though so it might be best to ask on the FTC Q&A and link the adafruit website not the ebay one.