The OE tires are NOT runflats. This applies to both the 18" and 19" M3 tires. Roadside assistance or patch kit and compressor, or compressor and sealant would be options. Putting a spare in the trunk works too, but adds weight and takes up space.
Tire Rack carries the ContiComfort Kit, which you can find in our Other Products section.
http://www.tirerack.com/a.jsp?a=AW8&...ries/index.jsp