i haven't tried this yet, but it looks like a mic on a regular 3.5 mm jack.
those are easy to find, like on Amazon.com
http://www.amazon.com/Olympus-ME-52W-Noise-Canceling-Microphone/dp/B000MYPPPE/ref=sr_1_2?ie=UTF8&qid=1343582603&sr=8-2&keywords=olympus+mic for instance.
I've been actually looking at this mic and similar ones since I first got the radio because I think the stock mic is garbage too.
Let me know if you try it and it works.