I was confused by this mentor idea when I was younger. There are certainly cases where someone who is knowledgeable and well established sees a younger person with promise and actively guides their development. However, some if these relationships can be where the more experienced person just makes the makes available - with a lunch or coffee to just field questions.
In my case I remember thinking I wanted a mentor but did not feel I had that. It was only years later that I realised that I had spent tons of time with some people I really respected. During those times I absorbed massive amounts of their experience. I did not realise until years later how privileged my time with them had been. They were truly mentors but were never formal ones.
So in your case I would look around and see if there are any people you admire or at least think they are very skilful. Ask them to have a coffee and ask about what they do and what they find exciting and challenging about that. Do that with 20 different people and you may find one you want to spend more time with. If you look at each of the professors in your school and look at what research they are engaged in - that can make a great topic of initial conversation.
A suggestion - if you don’t find your classes interesting ask for permission to sit in on Graduate seminars or take a graduate level class- if you can’t take it for credit see if you can get permission to audit if you find the topic interesting - you may find more interesting people that way.
Don’t be afraid to meet interesting people outside your area of focus. Again talking to professors about their areas of research - even in business, art , music, history, anthropology etc. is worth a coffee. You may find people you click with who have no technical skills whatsoever- that makes for a much richer life.