Looks like Amazon has the deluxe in-stock.

https://www.amazon.com/Final-Fantasy-VII-Remake-PlayStation-4/dp/B07SJ2P1XC?tag=gamespot-preorderguides-20&th=1

Just spent one hour webchatting with Amazon about this issue. I got transferred back and forth between the same departments multiple times because they didn't know who to send me to. The sixth and last guy I spoke with told me that he couldn't find instances of any promotional offers, so I sent him the four pieces of evidence from reading this thread and searching online.

1. https://www.amazon.com/gp/product/B07SJ2P1XC/ref=ask_ql_qh_dp_hza (the Q&A question of the product page so he could see how many others are having the same issue)
2. https://imgur.com/gallery/0SKF3FT (the screenshot someone took of the preorder page before it was updated)
3. https://twitter.com/amazongames/status/1205552954150797312 (Amazon Video Games' tweet regarding the theme)
4. https://www.gamespot.com/articles/final-fantasy-7-remake-back-in-stock-at-amazon-but/1100-6466818/ (Gamespot's website which was one of the many sites that documented preorder bonuses)

The guy had the nerve to tell me that these weren't Amazon's links and I had to point out that the 1st and 3rd one were. I then told him that I doubted many people thought they were going to have this issue when they preordered the game almost a year ago, and didn't expect Amazon to update their product page and remove all the pre-order bonus information. Then he said he would forward this information to their Marketing & Promotions team which would get back to me within 1 business day.

Here's to hoping I can get this resolved, but I'm not getting my hopes up.

Yes it is-Check this out at Amazon.com Final Fantasy VII Remake - PlayStation 4 Deluxe Edition https://www.amazon.com/dp/B07SJ2P1XC/ref=cm_sw_r_other_apa_i_U50DEbWDZCEAR

apparently it was only for Amazon UK

That's not true at all. I'm in the US and got the theme with my preorder. It was specifically advertised on the Amazon page too, though going by that page now you weren't the only person to have DLC issues with Amazon support: https://www.amazon.com/dp/B07SJ2P1XC