It's in stock at https://www.wallpapersandborders.co.uk/Onyx-Wallpaper-6801-2-By-Today-Interiors

Thank you very much for your help. I wrote an email a few days ago and unfortunately they replied that they don't have it. I'll try asking again, because it's available on the website

These are our wallpapers. Maybe someone has leftovers from the renovation?