I have never done this, but it should be a reasonably simple thing to do.
Take the car to a used car lot and put it on consignment. They will sit
there and babysit your car, and show it to buyers. They will get a
percentage of the sale. You might get more money if you just sell it to
them, but these are questions you would ask the car lot.

You might try putting out feelers on bimmerfest.com and e46fanatics.com;
both have for-sale sections, and folks there always seem to be looking for
nice ///M3's, especially with low mileage as yours seems to be...

Rick Peeples