how to make matcha paste

Hello Maki (and everyone else out there)! Thanks for the awesome sites by the way, love every article and recipe! Anyway, i'm not sure if i should be posting this here but i recently bought some commercial mochi (made in taiwan as opposed to japan) and it tasted really good. Out of the flavours (azuki, matcha and peanut) I loved the green tea one the best so i looked at the ingredients on the back and it just simply stated the filling was made from green tea paste. I then searched the web painstakingly trying to find a recipe but didn't have much luck. Well, I did kind of but the recipe didn't seem (by seem I mean I didn't try it out but rather judged the ingredients) to be able to form a paste-like consistency just like commercial tsubuan's (it was just add water to matcha powder.) So I just want to know whether you have a certain way to make the paste to deem it appropriate to use as a filling for mochi? By the way, I've heard that matcha and green tea powder (from other countries) do not give the same taste, is it true? Thanks a lot!