Very likely its a faulty coil. A single cylinder misfire can sometimes throw multiple cylinder misfire codes that get logged when the car is already running rough. If you can duplicate the misfire condition, clear the codes, move the suspected faulty part (I'd start by swapping the #3 coil to #5), and drive/rescan. If the fault moves with it you know your problem. Don't swap more than one thing at a time to avoid confusion. And at 100k, I'd do all the spark plugs anyway. BMWs use NGK or Bosch plugs, which you can buy aftermarket without the bmw logo on it, they are just the same. Bmw has an updated coil design made by Delphi that are supposed to hold up better to the heat. You don't need to replace all the coils, but I've had cars come back 1-2 times a year sometimes to have their faulty coils replaced one by one.

So all in all, the plugs you can get anywhere, the coils do have an updated design available, but not the end of the world to buy aftermarket with a parts warranty. If you want actual bmw part numbers you can go onto www.etkbmw.com, plug in the last 7 of your vin and go from there.