Zevia is quite tricky to get in the UK (not seeing any Vanilla Cola imported here) but if I see an opportunity to get it imported, I’ll go for it.
Tangentially related, Amazon has a lot of Green Cola, don’t know if that’s a brand people know or not but they claim to use stevia as well. Edit: Green Cola does contain sucralose so if you’re trying to skip that one too, keep that in mind.
What brand, if I can ask? Over in the UK I’ve only seen Dr. Pepper USA do cherry vanilla, which is different to Coca-Cola’s Dr. Pepper that uses aspartame and sugar. (US Dr. Pepper uses HFCS) UK Dr. Pepper was way too strong with the sugar but with the aspartame it just tastes watery and dead.