Schroth makes them - the only thing that makes most harnesses "illegal" is the lack of a big red button that says "PUSH" so that the EMT's can extract you quickly from your smouldering wreck. It's got nothing to do with the number of restraint points. (Also, the letter from the NHTSA) lever-style Cam-locks and Latch devices are basically what make most harnesses non-DOT, because they are designed to be less likely to come loose accidentally. Pretty stupid, but them's the rules.
Schroth makes both the "Rallye" style tuning belts, and the full ASM 4/5/6 point harnesses with street legal push style buttons. The "Profi FE" series 4-point belts (upgradable to 5/6 point) are street legal (For rally cars that must also be street legal in North America)
There's also a fine line between what is technically legal, and what will get you harassed.
Lastly, there's the visibility issue being clamped to your seat by a harness. Schroth also has 3/4 point harnesses that use inertia reels that can also be locked using a switch.
Quoting mj_rosenfeld:
Schroth makes street legal harnesses. I used them on my Datsun Roadster.
Mike R.