Ally, most DIY/hardware shops should be able to help you out with a set of washers.
You don't say what board you have so I can't tell you the size of washer you need, but it shouldn't be impossible to find somewhere that does the job, even if it's resorting to screwfix direct
EDIT: Just noticed it in your sig. Excuse me while I find my dunce hat...
EDIT2: Skate trucks have a 10mm axle by the way, so you'll need washers about that size.