I did look at the Sena mic but I need to find a standalone unit and not the whole Bluetooth set. Help appreciated!A quick search says that the mic plug is a 2.5mm, and the mic I saw from Drift has a stereo connector. So, if it is a 2.5mm, the Sena 20S mic, or any other 2.5mm mic would work with no modification. there is a chance that they have a weird wiring scheme with a mono mic connected to the right channel of the connector that would make a standard mono mic not work, but I'd doubt it. Either way, you could custom wire any mic to a 2.5mm connector (per the video) and get it to work.
I learned today that there are other bluetooth units that come with 2.5mm mics. @Skarcrow has one and the wired mic looked to be great quality. I don't know if you could order a standalone mic from them though. @Skarcrow, could you post up which bluetooth unit you have?
Edit: The connector is certainly mono. No adapters for any other input.