I wouldn't bother, especially if you would be paying for the tutoring. Oxford interviews aren't really something you can study/practice for (apart from developing confidence) as they want to see how you think and you will send reading material that you've never seen before about a week before your interview. My school set up a mock interview for me which was a guy quizzing me on my personal statement and was nothing like the real thing. Example questions I was asked in my interviews (for law) were "what is your favourite non-academic book and how has that influenced how you see the world?" and "what is your most controversial view?". I spent a solid 5 minutes of my 20 minute law interview discussing Stephen King lol. Instead of paying for a tutor just get people you know to ask you fairly abstract questions and see if you can prepare answers to them that bring in the subject you want to study.