There was one on trademe a while back, missed the end of the auction so don't know what it went for. It was a real old one without the rubber top/bottom on it.
He only had 10 litre ones. He advertised the original ones as 5 litre but later apologised and said they were 10 litre. I was the person that bought the one for $33. It arrived today and looks to be in good condition, he pressure tested it before he sent it. I think he's got about a dozen left.
The guy posts a picture on his auctions. I'll take a picture tomorrow and post it here. Yep, they are standard Corny posts. Kegs are pretty old, 1973 mine was made but looks to have been well cared for. It's a Firestone keg. Just tried a gas disconnect on the inlet and it's standard. The lid is a different shape to the standard Corny Keg but the O ring gasket is the same size so there shouldn't be any problems there.
I'm quite wrapped, it's a cute little thing and I think it will get on with the big boys ok. I mainly got it to use as a line cleaner, but it'll be quite handy to take to parties. I'm going to look for some wet-suit material to make an insulating jacket for it.