Good evening. I don't want to cover familiar territory for you, but have you looked at the Dutch Jewish Genealogical Database (dutchjewry.net)? There is a great deal of information relating to the Portuguese Jewish Community in Amsterdam, particularly the Portuguese Cemetery records. There are a number of "Gabays" appearing in various "formats," such as Gabay, Gabai, Gabbai, Siprut de Gabay, Gabay Henriquez, Gabay Correa, Abengabay, Gabat Faro, etc. That may be the hard part--figuring out whether your Gabay was a variant of one of these other variants. It is my understanding that the surname comes from Hebrew--meaning a trustee of a community. Ibn Gabbay was a jewish family name in Arab lands (Abengabay is a variant, I think). Hope this helps.