My best friend grew Shitakes on a large scale for sale at the farmer's market. First off, it is a lot of work. We were constantly on the look out for suitable logs which had to be cut and brought back to the grow site. Next each log has to be inoculated, laid out to rest, watered regularly, and eventually watered to induce the mushrooms to fruit.
And like all agricultural pursuits you need to be there to manage it. Going away for a few days when the logs are fruiting is out of the question unless you can find a friend to take over while you are gone. (They fruit as long as the weather is warm)
Mushrooms are the squirrels favorite food and you can plan on a constant battle with the little rascals to keep your harvest. We used nets and even constructed structures to protect the logs.
If you just want a few for home use look up sites on how to grow them using plastic tubs and cardboard. There was an article on this in last Sunday's Charleston, SC Post and Courier you should be able to access. Your local county Extension Agent may also be a helpful resource.
As for the original question about a discussion group or web site I would ask one of the vendors who supply mushroom spores for inoculation.