This link in 2007 talked of Quan in Carrickbeg, Carrick-on-Suir, Co Waterford from 1799 onwards and The Quans who left Carrick in late 1800 who finished up in Chicago. Perhaps these are not your Quans but may be related. Thomas Francis Meagher is very well documented but noone goes further than his Mother with the ancestry. Noone documents any brothers or sisters for Alicia.
http://www.rootschat.com/links/08mj/ It would seem unlikely that early US records would show the actually place of birth, normally they just say Ireland.
This article on the 100 year celebration of the Granville Hotel. Waterford refers to Thomas Francis Meagher and his Mother being a member of the Quan family.
Welcoming guests at the celebration included representatives from the Italian and American Embassies, Ken Power Historian with the Thomas ‘Francis’ Meagher society in the US and Christian Stevens a historian from Montana and now a lecturer at University College Galway.
Perhaps it could be worth contacting the Hotel or the people mentioned.
http://www.rootschat.com/links/08mk/http://www.rootschat.com/links/08ml/ Apparently there is a book:-
THE IRISH GENERAL: THOMAS FRANCIS MEAGHER. It is a complete biography, and goes into some of his family history. The book was published in September 2007
Thomas married Alicia Quan at her parents' residence that later became to be the Commin's Hotel. It was in this house that Thomas Francis Meagher was born to Thomas and Alicia on August 23, 1823.
http://www.rootschat.com/links/08mm/