Spare parts are also a pain in the ass to find,though if there is a KSC branded MP9 you can buy spare parts for that(Same gun,KSC is JP version) From Pulse Airsoft.
I think you can buy parts straight from kwa? If not they're reliable anyway so I wouldn't worry hugely. Ra-tech probably do stuff too.
KWA parts can be bought from KWA in the US,I don't see why it will not work in europe. KWA can't ignore such a large market. And yeah,they are really,really reliable,so in all honesty it's going to serve for a very long time before anything wears out.