Are you really stuck about where you could go and do your work experience? There are a number of choices you will encounter, which sector, public or private, new area or the same, large or small firm, salary, experience avaiable etc. A top tip is to leave as many options as possible open , especially when you start looking, as you never know what could be offered.
Finding an internship or placement, no matter how long, requires some work on your behalf. Firstly, you need a strong CV, then you need to find companies you are interested in, compose a cover letter, send it to them and wait.
Waiting is quite hard, limiting your possibilities to only one or two placements could be a little risky, it doesn't take an economist to work out that if you apply for a few you are more likely to be offered an interview.
Finding a placement is much like finding a real job. If you have successfully been chosen for interview (well done!) prepare some 'model' answers. After an interview it is likely you may have a day at a training centre where assessors will watch you. Obviously all companies have slightly different interview procedures, large firms often have training centres whilst smaller firms may have a rather intimate interview process.
Now you need to find a placement.
Economics is a diverse and varied subject allowing you to go into many different areas. In terms of finding a placement, this could be more of a hinderance then a help - simply because there is too much choice! Apply for a few (making sure you cover letter is company specific every time) and see what happens.Try your University's Career Service, they will be able to give pointers in the right direction, also try scanning the internet - this can be laborious but rewarding if you find what you want.