Help. Injector problem.

Hi. I have recently bought a 5.7lt gmc diesel V8. On overhauling the engine, I have discovered that one of the injectors is not working properly. Here is the problem. I don't know where I can get a replacement injector. I don't even know what sort of injector it is. I attach an image. If anybody knows what it is, or where I can source one I'd be very gratefull!!

Ok, I don't know how to post a picture on here. I can e-mail the picture. I'm really stuck with this problem, and any advice would be very welcome.