have you checked with your work that they mind, bearing in mind they will also be paying you for this holiday?
Also they might not want you to anything either in direct competition or tarnishing the name of your job.
you could try a n agency although they might not be interested if they know you wont be able to work beyond a week
bear in mind that you will pay a whopper of tax on a second job
Realistically, in order to be able to sort out tax etc in such a short time, you might need to look for cash in hand stuff. The only thing that springs to mind is either doing car boots, ebay, or door to door washing cars etc. If you have a skill (eg bricklaying) you might ask your family if any of them want you to do cash in hand stuff