advice about growing mushrooms

Not sure if any members here have any experience in growing mushrooms, but here goes: I have decided to grow mushrooms while waiting for the weather to get warmer in order to go back to growing vegetables. My problem is that I cannot find compost for mushrooms and I don't have the time/space/will to prepare my own compost. When I google "compost for mushrooms" what usually comes up is spent compost from mushrooms. Any ideas where I can get some? Do gardening centres usually sell this? I am quite happy growing oyster mushrooms on straw, but I would like to grow some portabella which grows on manure. Any links to sellers will be appreciated

 

@Zigs worked on a mushroom farm for a while, so I'm sure he'll be able to help. In terms of compost though, its fairly easy to find out what is in mushroom compost. Many of the ads for spent mushroom compost describe the origins and process. I seem to recall its a blend of horse manure, chicken poo and gypsum. Spent mushroom compost is all of the above that has been used for a single crop of mushrooms, then turned out to the compost heap to rot further before being sold. Based on that, I suspect you could make it by contacting a few local farms or riding schools to get some nearly fresh poo. I'm not sure what the gypsum does, unless it is to neutralise some of the acidity found in fresh poo.

 

All we used was fresh 'orse poo and straw, the heat from the decomposition helped the mycellium to grow, but we backed that up with 2 56kg propane heaters for the tunnels and kept the floor wet to keep the humidity about 98%

Once the mycellium had filled the bags we "cased" them, which is putting a 2 inch layer of peat mixed with lime on the top.

The mushrooms grew up thru that

 

Why not buy a mushroom kit from a garden centre?