Multi Output Flyback Converter

Hi,
I'm doing a project on Designing MultiOutput SMPS.
I chose Flyback to be operated in DCM mode. With the following Spec.
Input : 85 - 265 AC
Output: 5V/10A, 12V/5A, -12V/1A & -5V/1A
Estimated Eff : 80%
Operating freq:120KHz

I managed to workout the Rectifier ckt, Filter ckts.
I'm stuck with the transformer design. I'm not sure what core to use, what MOSFET to use. I followed some design procedures (Eg. Fairchild Application Note AN4137) but they all using their own Switch-cum-Controller packages.eg FPS or TOPswitches. I want to use PWM IC UC3842 and MOSFETS(not sure which one to use) for this design.

Can someone pls help me ? I'm really running out of Time & Idea.

I doubt you'll be able to find a transformer off the shelf.

What's wrong with the cores suggested on the app notes?

The most commonly used MOSFET is the IRF720, why not use it?