aubertin is not a rare surname in france, if you want to know its repartition in france, visit the site :http://www.notrefamille.com/welcome/default.asp
it is in french, but if you type aubertin in the "nom" box (right-top) you will get the repartition of aubertin surname according 4 periods from 1891 to present. it seems that it is a name coming from the east of france.
then if you want to write to someone, the white pages at:http://wfd.pagesjaunes.fr/
give the adresse and phone of all aubertin in france.
all these sites are in french (sorry)
have you tried geneanet, familysearch,...