Hi Rhys,
I'm always in favour of sourcing stuff locally & not paying lots for someone else to faff about with it & bag it up.
I don't know anything about growing mushrooms so please keep us posted on how it works. Having said that, since putting local horse manure on my garden I get a great crop of puffballs every year - they grow at the edges of fields in the area so I presume the spores have come in with the manure.
Good luck & keep posting