Vauxhall Vectra injector problem

I am having difficulty removing the injectors from my car, they were seized into the head but after days of meticulous cleaning and perserverence I have managed to get them free enough to be removed with a sliding hammer however the one I purchased screws into the inner threads of the injector, I am wondering if anyone would know where I could purchase the hollowed out allen key to remove the internals of the injector? I have no idea where to get one?