In CC 1 and 2 there was no separate Prop category and any prop would be an accessory attached to the character.
This has changed in CC3, and I guess nobody realized before that props can not be loaded into the Appearance Editor. So that looks like an oversight.
If you have iClone, you can attach the prop to a character and then save it as an accessory.
You can then drag and drop that accessory on a character in CC where it will also show up as accessory which can be edited in the Appearance Editor.
Sorry, I don't believe that there is a more straightforward way.