For those that want a detailed explanation here it goes :
Usually all amazon sites no matter the region they share the same product code for a specific product , so for example on this occasion the listing was live on amazon.de before amazon.co.uk by a week or so (The product code was : B07339W2V7 on amazon.de so you could replace from this link :
https://www.amazon.de/gp/product/B07...?ie=UTF8&psc=1 the de with co.uk and get the uk link for the product , though because the temp listing wasn't even up yet you would get an error/not the product page you were looking for ).
Then all you have to do is to a put a program/ add on to search for changes on that specific page and have it refreshed every 5 or 10 seconds and alert you .
Likewise do the same when the temp listing is up to see when the product is live for pre-ordering . Hope that helps ! cheers