So, firstly, I build my own 64bit mono.  In that last thread, I said I was doing it off of their tar ball.

I updated that slightly.  I now maintain my own local "mac ports" port file.

Attached is the latest one I built.  It may need updating.  And at the very least, you probably want to update it to build into a different place than my company's directory on my systems.

Once it's built, it does create it's own pkg-config directory so you can use it in building python-net

You can try and build against the usual 32-bit mono distributions on OSX.  But it's usually a bad idea.  Python is usually 64-bit in most places you'd want to use it in OSX.  When Xamarin finally gets around to fully distributing in 64-bit on OSX by default, things will be easier and this part won't be necessary.