Go to this page and click on the CPU of interest, then on the left hand side you will see "ordering / stepping / specs" and click that.
If the CPU is not longer manufactured, it will state "Retired and discontinued" at the top of the brief.http://www.intel.com/products/processor/core2quad/specifications.htm
You can do the same for the other core2 processors.
As they are a previous generation then expect them all to be EOL soon.
Once their supply of stocks run low I'd imagine they will only continue to make a small amount of "special" models - like those used for high end PLC / Scientific / Military applications.