HP releases OS patches for HPUX twice a year. Few break-fix patches releases as on need basis. Here is naming conventions being followed by HP.
Patch name format is PHxx_yyyy
yyyy = unique number
From patch name you will be able to guess area of its impact so that you can plan your activities accordingly. If patch requires a reboot or not can be determined while downloading patch from HP portal itself or even by running swinstall command with -p (preview) argument.
HP patches are available on http://software.hp.com/ which will redirect you to HP software depot home. HP passport login required to download patches or software from software depot.