If you want to use the original MFOS design, you can very easily build or buy a bipolar 12V supply. I'm confused by what you mean by "It's biased so that ground is effectively 12V, is that right?". Here's a kit: http://www.paia.com/proddetail.asp?prod=9770R-12
There are hundreds of suitable schematics, kits, and ready-made supplies.
If you want to try to use this schematic with a non-bipolar (+V only) supply, you'd need to make some modifications. You'd need to wire up a reference voltage at 1/2 of the supply voltage and use that as ground, and use ground as -V and +V as +V. You also would probably need to add decoupling capacitors depending on what you are feeding into the circuit. I don't know of any other saw to tri converters off the top of my head.