You could look in a search engine for law firms in your area.
You could also look in The Training Contract and Pupillage handbook (I think it’s black this year).
More useful though would be the ****** site, which allows you to search for vacation schemes by region.
(I hope it’s ok to recommend alternative sites!)
Most formal vacation schemes will be on that site - if you are looking for informal work exp (typically in smaller firms) then an internet search for firms in your area may be more useful as these are generally ad hoc and you would have to write speculatively.
Good luck!