Gamebillet supposedly get their keys direct from publisher. If you're not sure about them though, you can pay a little extra and get from Fanatical https://www.fanatical.com/en/game/yakuza-0 £3.39 (I bought from GB anyway, so thanks)
The best £3 to ever spend.
At least 25+ hours of content here! Not the most sophisticated game in the world but if you need a lockdown timesink... ;)
Fantastic game! <3