Dear chailingleow,
Well, my congratulations with so challenging task. Definitely no one off-the-shelf splitter will work in such a big range. Your goal is close to my. Currently I design splitter for 5 to 5000 MHz. It is considered to be impossible, but almost 50 years ago one of my coworkers and teachers taught me an excellent engineering rule: “your eyes may be scared but hands are doing”. Since that I am using this rule and it really works. In your particular situation if you restricted to Wilkinson combiner solution there is only one way to build it: to use multi stage Wilkinson. I can roughly estimate you need about 10 stages and such a combiner implemented on high quality double sided Rogers substrate may be about 25 inches long. The book what I recommended to you is Peter Vizmuller’s "Systems, Circuits, and Equations". There are many other books, but this one is a good start.
If you are not restricted to Wilkinson circuit check RF transformer based splitters. They will not provide results as good as multistage Wilkinson, but will be much smaller and less expensive.
Best regards,
RF-OM