I've been trying in vain to find the birth and marriage certificates for my great grandmother, was hoping that some of the more experienced members in genealogy searches might be able to assist?

My GGF's name is DI PALMA ERNESTO (or De Palma), b. 07 April 1878, in Pratola Serra. He emigrated to the US in 1901 or thereabouts, and lived first in Pittsburgh and then in New Kensington/Arnold. He used the De Palma spelling in the US.
I have his birth certificate, as well as that of his first wife's, GUIDA GIUSEPPA - who died in Italy in 1911.
I'm certain that my GGF went back to Italy around 1907/08, and I think he brought his first wife back with him. He came back in 1909.
My GGM's name is MARIA DOMENICA CENTRELLA (or Domenica Maria), supposedly born on 12 December 1889, in Montemiletto. I have been in contact with the comune and they have no record of her being born there, there was a person with a similar name (and parents' names) but it is most definitely not her, as this person emigrated to the US a few years later, got married to a different person and had a family etc.
I checked in both Montemiletto and Pratola Serra for a marriage or birth certificate for my GGM and GGF, but have uncovered nothing.
In the 1913 manifest, it states that my GGM travelled under her maiden name with my GGF's daughters from a previous marriage, that her previous residence was in Montemiletto, and that she is travelling to stay with her husband, Ernesto De Palma, in Pittsburgh. I assume they were married in Italy.
To be certain they weren't married in the US, I used Ancestry.com and Familysearch to check for a marriage cert for my GGF/GGM in Pennsylvania and New York (where not only she disembarked but my GGF's former brother-in-law livevd), but there were none. It did turn up marriage licenses for my GGF/GGM's children though, but not for them.
I have nearly everything else related to my grandparents and my great-grandfather, but I just can't seem to locate my great-grandmother's birth cert or their marriage cert. It is very frustrating!
Are there any outgoing passenger lists online? I figured that might be one way to narrow down their marriage date, with my GGF's comings/goings.
I assume it was between 1911-1913, as his first wife died in 1911 and my GGM travelled to the US in 1913.
Any assistance is greatly appreciated!
thanks!