Calamsi is commonly known for its sweet and lemon like taste and it is good to refresh throat to cure cough and colds. Filipino Overseas Workers usually go back to their provinces during vacation and collects Calamansi from its backyard plantation, i guess you cannot find calamansi in any other country but only in the Philippines.
If you are in Manila, this can be found in any market or supermarket in the Malls, however it is now too expensive because it was harvested in the provinces area and delivered in Manila. In the provinces it is free and you can make calamansi juice in any time you want.