Casio FX-991ES 計數機

I don't know where to get this model in 荃灣. But you can find the best deals in 旺角.
Check out these two places:
a. Chung Nam book store ($148, warranted by Multi-M);
b. HK Electronic OA Centre ($139, warrented by Onflo).
http://www.hkeoac.com.hk/default.asp
Hope this helps.