have you checked out your schools externship resources?
We have a set of binders that are divided into different categories (Small Animal, Large Animal, Food Animal, Exotics, Wildlife, Lab Animal etc) that have information about different externships that are available and that students have previously participated in. Each one contains a summary by each student that participated in the externship that details cost, living accomodations, how they liked the externship, what they were allowed to do/not allowed to do etc.
I know that several students from Penn have done externships at RVC (i'm hoping to maybe do one myself!) and other private practices in the the UK. I would check with your school first and then definitely contact potential private practices over there once you've figured out your schedule/if you want to get credit etc etc.
Good luck!