I have the 2010 MT base. I removed the radio yesterday to help with replacing the bulbs on the rear window defrost button.

Once I exposed the area under my radio, I was able to locate and remove the Phillips/8mm screw/bolt that holds the radio in. My screw driver was not magnetized. Once the screw came loose, it dropped down the back never to be seen again. Now I did magnetize the screw driver and did not loose any other screws (although I did forget to reinstall one.)

Where did it go? I got out the long screw driver looking thing with a magnet and flexible shaft and shoved it everywhere I could but no love.
I'd love to get it back so that 1) It doesn't rattle around and 2) So that I can firmly reattach the radio to keep it from rattling.

 

Another option is to remove the radio again and then use a shop vac or similar vacuum and see if you can retrieve it that way. Some of the mini shop vacs come with small hoses and attachments that can get back in areas that magnets can't get to. I'd empty the vacuum before you try this, so you don't lose it in the debris in the vacuum.

If all else fails, the nearest Honda dealer should be able to provide a replacement.

 

Awesome idea with the shop vac. I did install the other screw that I forgot so this is all that is left to do on that project. It'll drive me nuts if it rattles. So far I can't hear it but I know it's right there ready to drive me nuts at any moment.

 

You'll probably never hear it...

 

I hear it now and I'm not even close to my car.