Internals wouldn't be a problem but it could be different for the receiver. I'd want to have a defence to be on the safe side before ordering from abroad.
Since they are individual parts I don't think it matters if someone is paying you for them, as far as I know the VCRA concerns complete replicas.
I agree it is a loophole, but there are quite a few already. I mean, there's nothing to really stop you buying an IF in the first place, because you could lie about your age. Somebody could just paint an orange gun black if they wanted. I don't think anyone has ever been arrested for illegal possession of one. If the whole idea was to stop violent crime, then all these criminals must be even more stupid than we think, because they can't even get a spray can.
If you were a serious criminal you wouldn't rob banks and stuff with an imitation...stupid law but hey it isn't hard for a legitimate airsofter to get a defence so I'm not complaining.