Highlight an area based on postal code [Google Maps]

I need to show a newspaper reach on my website based on postal codes. I have read that Google Maps doesn't have an API for it, so I tried to find some alternatives.

However, I found nothing. So I am asking you, what would be the best and fastest thing to do in this situation? Are there any vector maps that have the administrative boundaries already made? And that can be connected with postal codes?

Google maps example of what I need