The reason that retailers no longer stock IBM is purely IBM's marketing strategy. Their computers are still in very high demand, but they are bought through different channels. The reason being that the technology that IBM computers have makes them very expensive (often more than $1000 more for the same specs as a Dell) This includes things such as the ability to drop a laptop from 1.5m and not have a single loss in data.
IBM is the king of computers, simple as that. If i could afford an IBM (or Lenovo as they are now known as) i would definately buy another one (i had one previously)
Lenovo (IBM) are still highly regarded in the business sector, and you will find that many of the people who rely on computers day in day out use IBM. NAB (National Australia Bank) for instance use IBM computers for every single computer they have in the whole world.
You can still buy IBM, but yes you're right, you can't buy them through retailers, because generally the people who buy computers through retailers either can't afford an IBM or have no interest in its benefits.
Just some useless information for you all