Long story short - I replaced my girlfriends tires and I didn't bolt the right nut/washer tight enough and it fell off mid ride - I now have no idea where I could find a replacement.

Without taking it into a bikeshop, anything else i can do?

Bike: Save Up to 60% Off Windsor Fixie Singlespeed Bikes - Clockwork

PS - It was a nut with a built in washer.

Thanks