There was a reasonable supply of those things, i.e. they weren't made in huge numbers, but there aren't that many people chasing them. They show up on ebay or BST now and then. The N cell adapters are scarcer and more expensive.
I had one for awhile and never ended up using it much. Pretty neat, but the AAA form factor is great from the factory. IIRC I got mine for around $12 and a few AAAA batteries.
I don't understand why someone isn't making them. There seems to be a big craze for the N cell ARC. Is there a big difference in run time between the two?