I know there have been home made one's but are portable N64's avalible on the market yet?

Yes.  They're called laptops.   

I have two N64 I want to scrap and turn into a portable, system. The instructions is up on the web somewhere. You will need.

1. A dependable battery unit, not a labtop battery.
2. A display of your choice,
3. A controller you can break apart.
4. A N64 unit
5. Conductive wires
6. Insulative non magnetic tape.
7. Molding etc ( this is only after you can get the unit small
enough,
8. Heat sink ( what makes these game systems big is the heating insulation.
9. RF components.
10. Sodering iron and sodering parts

I think that is what you need asides the tools, and a videocamera to record your progress. The only problem for me is the battery type. which wire to cut to go out to video, with or without RGB.

You can practically see the tear down of the whole unit itself, for that and any other game console.

.......

I would love to do an Atari sping loaded portable.
I have a 2600 junior lying around.

.........

then of course I have the unofficial NES to SNES piece but I dare not mod that.

PSP sucks. People brought it thinking it was
a better gba. In fact that is what the PSp
another GBA. What sucks is how now they
made a PPC that emulate PSX, when PSX can
run on PSP