Rule of thumb is that manufacturer will produce and make parts available for 10 years after production has ended. Now they will not sell all of it right away so parts usually linger through warehouse and dealer stock years after that. Complete engine, I imagine soon after they stop production there will only be a handful left.
IMO if you drive your M3 (or any high perf cars) hard or has power adder plan on bearings and rings job as a preventive maintenance. You have to pay to play.You also have to stay on top of things. One big downside of not having an oil dipstick is that its that much harder to check your oil. Not only level but condition. I myself change oil after every track event.