Several resellers say the Cube is unavailable from distributors, a sign that could mean an upgrade is coming or that Apple has decided to kill off its slow-selling machine.
"It wouldn't surprise me if they are going away," one reseller told CNET News.com.
Others said the same dwindling availability often precedes an upgrade, as has been the case with recent improvements to the iMac.
An Apple representative declined to comment.
For the past month, the resellers said, the Cube has grown progressively less plentiful from distributors.
However, all models of the 8-inch, cube-shaped machine are still listed as available on Apple's online store, and resellers can still get built-to-order machines directly from Apple.
The Cube has been a disappointment since its introduction last July, vastly underperforming Apple's plans.
The company said in February that it had expected to sell three times as many Cubes as it had so far.
Nonetheless, Apple executives said at the time that they planned to keep selling the Cube.
"The Cube has found a definite market," chief executive Steve Jobs told financial analysts.
"The disappointment to us was the market wasn't as big as we thought."
Amid a glut of the Cubes, Apple shipped just 12,000 of the machines in the January-to-March quarter, down from the 29,000 units it shipped in the quarter that ended in December.
Guernsey Research analyst Chris LeTocq said it is unclear whether Apple is looking to kill or improve its boxy desktop.
"Do they need a high-end consumer product? Yes, they do," Le Tocq said.
But LeTocq noted that in addition to slow sales, the Cube has had mechanical issues and a tendency for the clear case to have fissures.
Consumers complained that these were cracks, but Apple dismissed them as mould lines. If Apple were to drop the Cube, one possible replacement would be a new iMac based on a flat-panel monitor, LeTocq said.
