"Y'all" is the famous southern US form of the 2nd person plural. The Brooklyn / Italian-American "youse" might be another.
While the existence and usage of "y'all" has been addressed somewhat thoroughly here: What is the proper usage of "Y'all" in southern American dialects , I've found nothing else on EL&U regarding 2nd person plural forms in other English dialects.
I know there was a dual form in Old English (Dual (grammatical number)) does that survive in any of the dialects in the Danelaw? Do Scots / Gaelic / Welsh / Australian / other dialects retain any type of 2nd person plural / dual in modern usage?