What sort of angle are you taking, out of curiosity? My first inclination would be to look at his court documents like the pipe rolls. The Pipe Roll Society has quite a few of them. You're lucky that John's court is actually fairly well-documented in terms of official records. Irish sources have a lot to say about John as well. Depending on what you're specifically studying, some or none of that may be useful to you, and if you're a little more specific, I can definitely point you toward relevant Irish material. But when you say you only have those four available online, does that mean you're only using online resources?