You might want to start a search by looking in the Ellis Island website as there were 3 GMAZs that passed thru Ellis Island to America.
10 in Social Security Death Index
http://ssdi.rootsweb.com
Several in USA phone book.
Croatia's phone book is listing GMAZ
My family name is Gmaz and we came to the US when my grandmother was a child, so probably about 1930 or so. She was from Serbia, or what was left of Serbia after the first world war. I hope this helps.