Visiting venues like Havelock Road, Liberty Plaza, Kandy (Galkanda Road), Dehiwela will fetch you some fruitful results.
One can find Sri Lankan girls, Russian prostitutes and other working girls operating in and around these places.
Prostitution has not become as severe a problem in Sri Lanka as in some neighboring countries.
If an individual is looking for prostitutes and sex workers in Sri Lanka, then he can visit the brothel based areas and several clubs where working girls are at times found offering their range of adult recreational and entertainment services.
However, you should still stay safe and a bit careful while dealing with situations related to sexual interest.