At this time it is necessary to set up separate affiliate accounts for Bookshop.org UK and US. We are looking at ways to sync accounts between the two in the future, and we'll be sure to make it clear if this option becomes available.
We are aware that there is currently a minor glitch which is preventing UK-based customers from reaching our US website by normal means. As a workaround, if you are trying to visit our US website, this link will direct you there.
From there, it will be possible to find the Bookshop.org US affiliate application (located at the bottom of the page titled "Become an Affiliate"). Please be aware that Stripe accounts for the US site must be linked to a bank card registered with a US billing address.