In 16 years of living in Puerto Plata I have never come across one - Dominicans in need of a suit will generally borrow one from any friend that might have one!!
What sort of suit are you looking to rent/hire & for how long? ~ Grahame.
the only thing i would suggest and not sure if this helps....sometimes the resorts will have suit rentals on site, i would hope somewhere along playa dorada there is some sort of suit rental place.....give it a shot