are you in London? If so you can go to the Dental School at KCH (Camberwell) and been seen there by a trainee under supervision - first come, first served - might be a bit of a wait.
You can also buy dental cement and try and glue it back on yourself as a temporary measure - I used to carry some around as I was paranoid about my front crown coming out for a while! It was difficult to track down, but think I got it eventually at that big chemist on Wigmore Street. It was in a travellers dental kit kind of thing.
Or try a private dentist? Might not be too expensive for a one off.
HTH