Hey,
You can find more information about 12v trains on this site, it is in Dutch so that isn't a problem for you: http://legotreinforum.forum2go.nl/ .
About missing parts you can buy them on BL but it is sometimes expensive, check ebay of other sites for a model that isn't complete.
A the moment I don't have spare engines but check on ebay and with a little bit of luck you can find one for 40 euro's. I never had to pay that much for a 12v engine.
You better check on ebay in Germany, there you can find more parts for 12v trains.
Greetings,
Christophe