Thank you for that hint, kronovan. I couldn't find anything, though. Could you provide a page number, please?
My bad, I was recalling my adds to the canon from my Duchy of Oriente campaign notes. There are Italian and Spanish speakers in the Duchy of Oriente, so I wrote in that people of Portuguese descent can be found in the Suva Archipelago of planet Fletcher, living among peoples of Italian and Spanish descent. I sometimes tend to get carried away with details in my campaigns, to the point that they get recalled as actual canon. :))
While browsing my Federated Suns Handbook last night for some campaign fodder, I came across a reference to Portuguese. According to a brief entry on page 135 in the Society and Culture chapter, Portuguese speaking peoples are living in some of the worlds along the Capellan March.