@bdev and
@Tag_ZA found aftermarket straps that look similar to the OEM Gulf F1. You can see their watches & straps in these posts:
https://forums.calibre11.com/thread...-you-wearing-wruw.19044/page-212#post-1330992
https://forums.calibre11.com/thread...-you-wearing-wruw.19044/page-398#post-1767637
FYI. Some people don't like the OEM Gulf F1 strap, as they feel its not comfortable. Also, the asphalt treatment of the leather material tends to show wear over time. Hence I've chosen to preserve my OEM strap and wear the watch with other straps.
I also wear mine sometimes with the C11 Monaco's Gulf calf strap, which I purchased for about $110 from an AD. So I'm surprised that the F1 strap costs so much.