Given an Ubuntu kernel package version how do we find the release it is from?
The kernel package version is of the following form 2.6.35-6.9. The numbers before the - represent the base upstream version from which this kernel was forked, the first number following the - represents the ABI number, the final number is an upload number. Taking the package version first remove the upload number, then round the ABI number down to the nearest hundred (which can include 0), for example:
2.6.35-6.9 => 2.6.35-6 => 2.6.35-0
Look up the final version in the Kernel/Dev/TopicBranches mapping tables (see Current Branches). Once you have the release and branch you can obtain the source.