Hi Mak

Not sure if you want help on tissue culture or cloning. Mostly cloning involves taking a clean (generally use the inside of a mushroom near to where it forms the spores, as this is the most genetically diverse part), piece of tissue from a mushroom that is already growing and then allowing it to grow on agar medium. The simplest way to get it clean is to clean the outside and then rip it open being sure not to touch inside. With a sterilized needle take/cut a small piece out and place on agar medium. If you see contamination (generally any green or other colored growth ) you will need to do further isolations until you end up with a clean culture. Once it has grown out and is only mushroom mycelia. After this you can start to reproduce it either in grain masters/suitable spawn material and then grow it on a fruiting substrate.

Also remember that the more clones you make the weaker the mushroom strain becomes. To avoid this you can make a large quantity of isolations from your first mushroom and store these with longterm storage like sterile water or oil slants. Then when your strain starts becoming "weak" you simply start the strain again with one of your cultures in storage.

I am not too sure of Cordyceps but try Stamets "growing gourmet and medicinal mushrooms" probably the best book to start with.

The above procedure assumes that you have access to some lab equipment, if not you will have to improvise and see what works best for you.
ciao