Only 20 inches around and they couldn't get it to fit? That's bullshit I once worked on a boot where the woman was 24 inches around and it only took about 2 hours of work to get her in a boot that fit her foot lengthwise and still accomodated the wider calf. Also props on losing that much weight I know how tough that is dropped from 280 to 165.
What I would personally look for is a low cut boot. I think it was either Salomon or Ride that had a boot with a low cut in the back for bigger calves and had a piece that was attached with elastic so it would bow out. If you can find a boot like that I would cut the elastic so this bonus piece pops out, then put in a heel wedge to raise you up slightly to fit your calf. Or you could try to find a liner-less boot they do exist I think Deeluxe makes an adult one and maybe Salomon. Or food for thought check out the DC park boot the liner itself only goes up to the ankle except on the tongue of the boot and with a heel wedge you might fit OK in the boot.