You buy or sell $ 50 Billion dollars [Took USD as an example] per trade? You may be confusing lotsizes. The standard lotsize on the fx market is $ 100,000 for the USD, but people confuse this as some brokers refer to a lot as $1,000 to make things eassier for their traders.
What do you want them to do? Just place a trade on the market based on your parameters, or find trades for you as well? If it is just placing a trade on the market you may want to consider the MT4 broker software, that enables to manage multiple accounts simultaniously.
If the $ 50 Billion is correct, I will quit my job and dedicate my time to place your trades on the market on behalf of you… Heck, I’ll even distribute them between brokers to cover your systemic and liquidity risk…