Barters are bought from a central pool
You have answered your own question. Even if you could find a way to do this in a trust-free way that was unable to be controlled by the governments, you still have the problem with whatever crony capitalistic bs happens with the fiat currency will affect the barter currency.
I think I have proposed a cryptocurrency that is the best of all worlds--decentralized, relatively stable, and efficient. See my signature if you would like to know more or discuss it.