[Pyros]

Hi,

I am not sure if this will work but try this:

While designing your scenario (editor), after you have bought any Belgium units try to alter the nationality of player's1 forces by selecting the US.
Now you will be able to buy units from the US oob while at the same time you will retain all the previous units in your forces list.
Now (while you have selected the US nationality as player1) if you press the button "ALLIES" and then you "set captured" you may buy any required equipment from other countries under the US flag.
After you finish this process, you may change in the main editor screen (once more) the flag/nationality of player's 1 forces by selecting the BELGIUM and you may buy additional Belgium units.

cheers,
Pyros

p.s I don't know if this will affect the game but you will probably get what you wish.