Go to www.numberway.com and look up Argentina telephone directory putting in the last name and click on TODOS (all) and Buscar (to find) and up will spring 11 chiavone, 100 Grasso and Sanfilippos etc etc...Select those whose address is in Rosario and then selct those whose firstnames are ibn the family and write them a letter in Italian for potential relatives (there are no spanish languiage smilar letters).
Form letters in Italian is www.initaly.com/gene/mem/letter1.htm
Use the telephone directory for Argentina where the zip code is shown since letters will not be delivered. Its like the USA where they had to resort to zip codes because they had employees who were unediated. Petertimber