Just an update, got the connectors from eBay. They are very similar to the MadVapes ones but they don't appear to be the same make. There are some differences.
Atomizers fit better in the eBay ones. The center post on them is better and the correct height. The MadVapes ones are slotted on top which makes them too tall. Atomizers have a large gap. The gap is correct with the eBay ones. The threads seem about the same in depth of cut and atomizer slop seems about the same between them.
The battery end fits better on the MadVapes ones. The threads are not cut as deep on the eBay ones so they are a bit looser in the battery connector, but not to the point of being a problem.
Overall length of the large and small ends is the same between the two makes, but the height is short on the battery end threads for the eBay ones. If you screw the nuts all the way down, they just spin around without any thread contact. The MadVapes connectors don't do that. Wouldn't normally be a problem since there's some thickness to the enclosure, but you'd need to add a washer for something like an Altoids tin.
The eBay ones have airholes in the side. Typically not a concern one way or the other, but theres no reason for them to be there.
Otherwise, the eBay ones seem to be a suitable replacement at a hugely better price.
Thanks again for posting that link. I'm sure I'll be buying more down the road.