in singapore, the top selling brand is Omron. (i used to be a nurse)
u see omron health care products everywhere.
the best range now should be the HEM 7121 but of course if you have better budget, u can try omron higher range product.
u can buy everywhere, from guardians, or watson, or the supermarkets.
if you prefer online, it is cheaper and delivery 2 days
i just bought last week from this seniorcare.com.sg
http://seniorcare.com.sg/product-catego ... -monitors/
do note that there are other brands in Singapore like Rossmax, panasonic, or tenasoval. but i feel omron is very good.