I found this trilogy to be the best for learning spoken sinhala,
It will teach you not only basic survival but will help you thrive.It also comes with a few audio cd’s with songs and pronunciation guide etc.
Also, the teacher doesnt teach you written sinhala form mixed up with the spoken,which usually is the case with all other older sinhala lauguage resources and can be problematic when speaking. She does teach how to read sinhala script,and that can be learnt quite quickly.
If you are a language magician, then these books will be easy for you.
If however you just want to survive (quite well),then the website ‘lazy but smart sinhala’ by Dilshan is good enough.
I have not come across or heard of any official Sinhala language learning centre.
I must admit that i attempted learning the langauge for five years but failed miserably. I was able to read,write and memorise hundreds of words quickly due to inspiration but the speaking part didnt work out too well for me. I received the above suggested books at the end of my inspiration and i believe that if inspiration arises again, those books will lead to complete fulflment in sinhala proficiency.
As a monk trying to speak sinhala with lay people,it can be quite difficult because nobody wants to correct me, and just agrees with whatever I say, therefore I can’t tell if what im saying is correct or not, so you can imagine the communication fun i experience.
Most western monks who have learnt,have learnt while staying with sinhalese monks,so as a lay person,i am sure you will be helped by everyone you meet.
All the best.