first of all you wont find a mediator to do this trade, and if you somehow did nobody would be willing to wait around for that all to come together.
second, your prices are very high. you would basically want to go below the FG to $ ratio, not triple it. People use these forums to get good deals or just fair ones.
third, the only way someone will trade you is if you go first 100%, and youll just have to hope they pay you