Way more than 6 left, I bet. I know at least three people with A680s! (One of them has the M4.) Surely the "ARM port of BSD 4.3" is RISC iX? And I don't recall the UNIX kernel ever being in ROM; even the M4 which was purpose-built to run RISC iX boots RISC OS from ROM, and you then boot the UNIX kernel with !RISCiXFS.