Good architectural firms in Singapore would look forward to leaving their portfolios on their websites, provided they have one. You would be required to check on the various kinds of projects that they would have handled in the past. It would enable you to determine the kind of services that you would receive. It would not be advisable to restrict your search.
You could search for an architect from another town, city, or in your immediate region. What matters mostly would be the kind of services you would receive. You could check on the directories in your region and try to find the perfect architect for your project.