Getting Moss for a Japanese garden

Hi, my friend has been asked to try to put together a japanese garden with a very limited budget (50 pound). They have a couple of small trees and rocks donated already but looking to cover the blank soil a bit and we know moss is used a lot in japanese gardens. If we buy a punnet of moss will it spread? It is a shady garden anyway. Any other ideas for covering soil and kepping it looking japanese on a tight budget? Thanks in advance????