My guess as to why they quit making them is that there aren't many games that support them. Gran Prix Legends and the NASCAR series of games by Papyrus are among the few I knew of that supported anything more than a sequential up/down type shift arrangement. Now that GPL has kind of fallen off the radar and Papyrus lost the rights to NASCAR, the demand has dropped off.
If you have newsgroup access, go to rec.autos.simulators. You might be able to find an Actlabs shifter there for a reasonable price.
Tim