In any event, I've always wanted to add a nice 3PO case to my collection. I just picked up this one from Mike at his shop on a recent trip to Toronto and although it wouldn't fit in my checked luggage, it made the trip back with me as a carry-on.
Interestingly, period catalog advertisements describe the C-3PO carry case as "life-size"! I guess that could well be the case, as it's noticeably much larger than the Vader case.
So that's it for these two cases. As noted, Vader cases are super-common but 3PO cases much less so. I did find a good use for busted Vader cases though - you can use a Dremel to cut off the hinges and separate the two halves of the case, polish up the front with Plexus or another quality plastic polish, and hang the front half of the case in your collecting room... or in my case, give it to your Star Wars-loving nephew to hang on his bedroom wall :-)