I know this is an old thread, but I just wanted to add that
attractiontickets.com actually has a US version of their site (you select it at the top of the page) where it will show everything in US $ so it seems pretty clear that US citizens can purchase from there. I did notice that you can’t see “combo tickets” (tickets that are for BOTH universal and Disney, +/- SeaWorld, Busch gardens,
Legoland, etc.) on the US site, but on the UK site if you put one of those in your cart and go to checkout it allows you to put in a US address. I emailed the company and they assured me that I can purchase from the UK site (see screenshot). From what I have read it seems some people have had trouble with the transaction being rejected by their bank likely just because a large overseas purchase is suspicious for fraud, but it seems like they have been able to work it out. I’m definitely going to look at this (or similar) sites for future trips.
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