Ralph and Bill: Pocket Greatest American Heroes
Mego did manage to sneak one Greatest American Hero toy into the market before shutting it's doors, albeit in limited numbers. (pics courtesy Chris DVM)
In terms of rarity, this set does crop up from time to time, although the show's cult popularity keeps the prices rather high. THe majority of boxed sets found seem to have "Kay-bee Tys' Stickers on them, suggesting that these were exclusively cleared out at that retailer.
"Now Available Ralph,Bill and Pam Action Figures. Poseable 8 inches tall and Fully Costumed. Only by Mego" If only that were true....