If you can get to a large city fairly easily, flick through the city papers or look online, a few of the Hong Kong firms like Raja Fashions mentioned earlier in the thread do UK tours where they will measure you up at a hotel room and make a suit for you.
I’ve been into Raja’s shop in HK and they are often recommended – i’ve never used them though. Not as cheap as it used to be, when I first started going out to HK regularly about 5-6 years ago you used to be able to get tailored shirts for £22 a pop and a good suit for £3-400, it’s easily 50% more now.