The reason why iPhone 4S and iPad 2 are not supported is because of the A5 processor chip used in these devices. The vulnerabilities used by hackers in non-A5 chips are fixed in A5 based iPhones & iPads. Hackers are continuing their efforts in identifying other security holes on iPhone 4S & iPad 2 but not sure on the timelines when they will be able to release jailbreak.
You can download the new untethered jailbreak from either Chronic Dev Team or The Dev Team.