What should I call a capacitive touchscreen stylus in Standard Chinese? I'm in China and would like to buy a stylus for the tablet I aquired a week ago.

I tried to explain to several stalls at a secondhand electonics market in Guangzhou today what I needed and nobody understood.

I know the word for 'stylus' in the sense used with touchscreens is 触控笔 (chùkòngbǐ) but there are different kind of styli for use with different kinds of touchscreen and the wrong type will not work.

How would I ask a seller if they sell the type of stylus I want to use with a capacitive touchscreen device? (The kind of screen an iPhone uses.)
In Taiwan it's called a 電容式觸控筆; maybe if you tell them you need i-phone 專用的觸控筆 they might get the idea.