Looks like rtsystems.com has software for $49.00.  :(  And it's Windows only software, too.  One route would be to borrow/eval a copy of that, install it on a VM along with Serial Port Monitor and get the protocol.  Then add support to Chirp and you'd give cross-platform programmability to everyone.  Maybe you're willing to make a $49 sacrifice to enable everyone?  I know a lot of people like CHIRP because it's a universal tool for all their radios.

Another route is to "fuzz" the radio.  You could form your stimulus with the existing Alinco radio to speed things up a bunch.  It looks like the protocol for most models differ pretty minimally for a given vendor.

You're right: Serial Port Monitor is Windows only.  Unfortunately a lot of the OEM programming software is Windows only as well.  FWIW, Serial Port Monitor did do a really nice job of documenting the protocol.

I'm not a Windows fan, either.  I don't even use it for work much.  I used a Windows 7 VM for the initial protocol snooping, and then carried out the remaining dev in MacOS and Linux.  It's pretty easy to "pipe" your USB serial dongles from the host to guest OS with VirtualBox, for example.  I'm sure other VM technology will do this as well.