I dont think it will be a problem to run it until you find super, personally.
It will take a lot of running to start noticing any long term ill effects, and mixing then replacing with super later will be fine.
You could try looking for the additive to counteract any effect, i am sure halfords or other factors will have it, or some of the larger garages.
The main problem for most cars is long term storage with fuel, not the short term running.
Just drive conservatively and listen out for any det under load, just in case.