Found all sorts of original series prototype stuff on eBay. None is from me…
Safari Joe arms: http://www.ebay.com/itm/Rare-Vintage-Thundercats-LJN-Prototype-Casting-Safari-Joes-Arms-/150681443261?pt=LH_DefaultDomain_0&hash=item2315505bbd
Mongor head, arms, and 1 leg: http://www.ebay.com/itm/Rare-Vintage-Thundercats-LJN-Prototype-Casting-Mongors-Body-/150682715214?pt=LH_DefaultDomain_0&hash=item231563c44e
Capt. Cracker head, 1 arm, sword, and legs: http://www.ebay.com/itm/Rare-Vintage-Thundercats-LJN-Prototype-Casting-Captain-Cracker-/120799244870?pt=LH_DefaultDomain_0&hash=item1c20323246
Moat Monster head and arms: http://www.ebay.com/itm/THUNDERCATS-RARE-1980S-CAST-RESIN-PROTOTYPE-HARD-COPIES-LJN-TOYS-/250919622511?pt=LH_DefaultDomain_0&hash=item3a6bf9976f
Moat Monster wings: http://www.ebay.com/itm/THUNDERCATS-RARE-1980S-CAST-RESIN-PROTOTYPE-HARD-COPIES-LJN-TOYS-/260881267016?pt=LH_DefaultDomain_0&hash=item3cbdbc3948
Ben-Gali hammer: http://www.ebay.com/itm/THUNDERCATS-RARE-1980S-CAST-RESIN-PROTOTYPE-HARD-COPIES-LJN-TOYS-/250919354705?pt=LH_DefaultDomain_0&hash=item3a6bf58151
Jackalman’s shoulder armor: http://www.ebay.com/itm/THUNDERCATS-RARE-1980S-CAST-RESIN-PROTOTYPE-HARD-COPIES-LJN-TOYS-/260881280489?pt=LH_DefaultDomain_0&hash=item3cbdbc6de9