You may be right about them not being "rare" since many were probably made, although at $350 each in 1984 dollars nobody was likely handing them out willy-nilly, even at IBM itself. And since they are "weird" and cannot even be plugged into any contemporary computer, I would guess that most of them have gone into the trash.
When Soarer's converter came around last year, I started looking for them. I have bought a few, and watched them go by on ebay. At first, you could get a nice one for $20-$30 + shipping. That did not last long.
My observation is that now they are turning up less than once a month, and bringing anywhere from $35 to $150 plus shipping.
