http://github.com/beagleboard/kernel has older kernel revisions, including
3.2. However, note that the patches to support BeagleBone Black are not
included in the beaglebone-3.2 kernel patch series.
You can use the TI 3.2 kernels from the SDK (
http://elinux.org/Beagleboard:3.2_SDK_On_BeagleBone_Black) or Android (
https://gitorious.org/rowboat/kernel/commits/03f2a1e9ea7f8b11ff6809f5a75b614011f8adb6
).