I don't honestly know who you need to contact at RVC, but you could try emailing registry (registry AT rvc.ac.uk). If it's pathology you're interested in, I'd probably just email Ken Smith, head of pathology (find his email on this page:
The Team - Pathology and Diagnostic Laboratories - Royal Veterinary College, RVC). He's super nice and I'm sure he'd be able to point you in the right direction.
Just so you know, pathology is a 1 week long core rotation at RVC, with a mix of clin path and anatomic path. There's also a tracking rotation that's 2 weeks long (I think they do a mix, too?). Best bet is to email Ken and discuss what you'd like to do.
If you do end up coming, ask me about housing stuff later on.