where can i find a plumber in hk to unblock my toilet?

If you want to unblock the toilet yourself, you may buy a toilet pump grocery (like Japan Home) or you may buy a box/jar /can of pipe cleaner (eg. Pipeman by LION) from any Supermarket (usually it is placed nearby the detergent); follow the instruction and you may solve it yourself.
Otherwise, you may get a plumber from the store which sells taps or bath tube nearby your flat, they usually can refer one to you (they usually goes with a word "通渠"). You may also try out with the two telephone numbers below:
Kam Fai (serves Kowloon Side, Mainly TKO district)
Tel:2719 8771 Mobile: 9098 0498 E-mail:[email protected]
Mr. Plumber (Contact: Mr. Lui)
Mobile：90921463 Tel: 25441823

It may cost you from $500 to almost a thousand, it depends on the difficulties of the duty. If it is only a simple task, it takes around 30 min. If it is so difficult it may takes around one day, you may quote the price from the plumber first before they start.
Hope this information may help you.