I want to know if any of you know what the fastest way is to change USD into BTC for large amounts? Coinbase and most exchanges offer ACH and wire for large amounts but takes about 5 days to clear, which is what I am trying to prevent.

I know I can buy using VISA/Mastercard and have it immediately, but that is for low amounts.

Does anyone know of a service that changes USD into BTC quickly for larger orders?