Contacting university after graduating for help contacting a professor who isn't replying to emails I'm aware that this sort of idea gets asked a lot, but I'm slightly stumped by what I'm allowed to do and what's considered bad practice.

I had been in contact with the supervisor of my Final Year Project, the person that most likely knows my abilities best after my three years of university, who'd said he'd happily write a recommendation letter for the MSc programs I was planning on applying to. However, for the past several weeks I'd been trying to contact them to no avail. I've left a few email reminders, and two phone calls. I've been told I should contact the Head of Department or someone above them at the university to talk to them.

Is contacting someone above them considered rude, or bad practice? 

This professor has a history of taking a while to respond. I tried contacting them early to ensure I would give them enough time to write the letters, but time seems to be flying past as they no longer reply.

I may have the possibility of going back to the university (I'm currently doing an internship in another country) and possibly set up a meeting, is this something I should definitely do given their tendency to be bad at replying to emails, or should I contact their superiors?
you should not contact the head of the department or any other Prof. just to get in touch with a professor, that is just a bad idea on many different levels.

If you are really desperate, I would perhaps send an email to one of his PhD students and ask if he has been around for if he is on vacation. As another resort, you could try calling the secretary of the department and ask if they have seen this Prof. around. Client physically to the professors office does not seem like a good idea either, unless you set up an appointment. If you know the professor well enough that I would perhaps consider just calling his/her office number directly and during office hours. some people acknowledge that they are bad at answering emails, so in that case I do not think he would mind a cold call.