https://archive.is/PUk3 <--- This posting describes the different collections that Google acquired or received. Is there irony in that one needs archive.is (archive.today) to access it? Maybe someone can find the original still accessible?
I'd also be keen to know. I had assumed it was https://archive.org/details/usenethistorical .. which is pretty good, but I just discovered comp.lang.javascript only goes back to 2001 there, so my posts from the 90s are not to be found :) Other groups do go back to the mid 90s, however.