If the Forebears website is to be believed it's the most common name in Portugal. Unsurprisingly as a consequence it's also hugely common in Brazil where there are over 4 million Silvas!
Not as common as I assumed it would be in Spain (111th most common name) seems like it is much more a Portuguese than Spanish name so Bernardo is a common or garden Silva but David is a little bit rarer!
Re. Antonio, I guess we'll be keeping tabs on any significant emerging talent and we've done good business with Benfica before but this seems like a huge stretch to me. Feels like the website jus padding out a bit of content.