yeah its been removed, heres how to do it if i can remember.

go to C:\Program Files\Steam\steamapps\common\supreme commander 2\gamedata and open up uncompiled_lua with winrar.

inside the archive open uncompiled folder then maps then SC2_MP_007.

extract SC2_MP_007_scenario.lua somewhere.

look for a line that says mappack = 1 and add -- in front of it to ignore the line, you might be able to delete it but i just put the -- in front.

add the modified file back into the archive by dragging it to the winrar window.

rinse and repeat with folders

SC2_MP_103
SC2_MP_301
SC2_MP_303
SC2_MP_304
SC2_MP_304_1K

I cant access that page, iit may of been removed. Can someone check plz

how to unlock pre order maps http://forums.steampowered.com/forums/showthread.php?t=1210474