One of these might be helpful: https://rapidapi.com/collection/geocoding-location-apis
You need the Map object part. But I do wonder in you could retrieve the boundaries from the Google database. You can use it to create your own boundaries on top of the Google maps data. But my guess is that Google would protect its data and you can not freely retrieve the boundaries that are shown visually to the end user.
Some countries have open databases where you could retrieve such data but I do not know if such databases exist for Singapore.