I'm finishing up the first version of the software now, and will be sending it and a prototype mic/amp to a watchmaker friend.
I still haven't decided on a distribution scheme. Most likely free and pro versions of the software, and the pro version can also be purchased bundled with a mic and amp.
For those who urgently want to build their own now, the mic element is a 27mm piezo disk, readily available on eBay. Power is provided by a 9V battery, which is good for about 50+ hours of continuous use.
Here's the current version of the circuit I'm using, along with a stripboard layout. Please don't redistribute it on other forums and such for now.
This amplifier will work with Biburo too, but I've found Biburo to be pretty bug-ridden and unreliable, which is one reason I decided to write my own software.