XDA is the holy grail of Android development. For almost every major phone from 2012 (Samsung Galaxy S2, S3, Note 2; HTC One X; LG Optimus G; Sony Xperia T), XDA has dedicated threads with verified MD5 hashes for stock firmware.
. However, most hardware from that era cannot support newer versions of Android. Google Help How to Manage an Android 4.1.2 Device Today android 4.1 2 update download