That strap is a total fake! The eBay seller may not be aware of this.
(And I may win the $163,000,000 PowerBall jackpot on Wednesday)
Below are scans from Rene Rondeau's book THE WATCH OF THE FUTURE. They show what the front and back of an original two-tone strap should look like.
For members with small screens, the text reads:
"The original two-tone "Ventura" strap had a stripe of 24K gols applique, as indicated by the stamping son the back. It was fitted with a Hamilton-signed 14K solid gold buckle.
Reproductions have been made in recent years. Those marketed by the author are clearly stamped "RENE RONDEAU" to ensure they cannot be passed off as original. However, an unknown supplier has reproduced new straps stamped (illegally) with the Hamilton name, and a crude "H" logo. In addition, these are stamped "electric" while the originals were never marked with that word. These Hamilton-signed replicas have been sold as original to collectors unfamiliar with the real thing.
The reproduction straps can be easily recognized by the fact they are lined with tan kidskin and have two narrow keepers rather than the single wide style of the original. Also, they have been made in either 17mm or 18mm metric width, whereas the originals were marked 11/16".
Outside of lucking onto an original strap on the Swamp, I can't offer many suggestions. Ideally, you would go to the NAWCC and find out where and when there is a watch collector's show being held close to you. Go to the show, visit the booths, and hope you find a collector with a strap for sale (or knows where you can score one).