Sony Japan has just announced that they have a production issue on the Sony a7S III. So it may take some time before Sony a7S III is delivered. You can pre-order Sony a7S III at Amazon & B&H & Adorama & Focus Camera.
From Sony Japan:
Notice and apology regarding product supply of digital single-lens camera “α7S III”
Thank you for your continued patronage of Sony products.
Due to production reasons, it may take some time before the product is delivered for the digital single-lens camera “α7S III”.
We are currently making every effort to meet the needs of our customers, so please wait for a while.
We deeply apologize for any inconvenience caused.