Dutch Jewry is a useful website for starting. In the left-hand column under ‘Amsterdam / Mokum’ you can find ‘Portuguese marriages’. Lower down the column you can find ‘Portuguese-Israelite cemetery Beth Haim’. Remember that whilst Amsterdam was the largest and most important community, it was not the only one.
Amsterdam Sephardic Marriages
Weddings in Amsterdam also needed to be registered with the civil authorities. This is extremely useful because these documents state the bride and grooms places of birth, information absent from kettubot.
The archive of the Portuguese-Jewish Congregation of Amsterdam is now in the Amsterdam City Archives, pictured below. There is a Dutch-language index of the collection at: https://archief.amsterdam/inventarissen/overzicht/334.nl.html (use Google Translate!). The collection is being digitised and copies of documents can be bought online. A transcription of the Livro de Bet-Haim do Kahal Kados de Talmud-Torah can be downloaded for free at: https://www.amsterdam.nl/stadsarchief/archief/downloads/beth-haim/