Good on you fluffy for wanting to earn a bit of money.
When I was 14, I got a job waitressing. I worked most Saturdays and most days during the week when I was holiday. I was there for about 5 years (until I left college and got a proper job).
I know my friend who runs a health food shop really values her Saturday girls. The customers love them and they provide lots of cover in the holidays, so perhaps try smaller shops to see if they can give you anything.
Do your parents know anyone who could offer you some part time work?