Mycelium can be cultured in a liquid (as opposed to a solid like vermiculite/brown rice flour) which you can then use to easily inoculate substrate and start mycelium growth much faster than if you were using spores.
You should first go to your local homebrew supply store and buy the lightest colored powdered malt extract they have. Mix 4% (by weight) malt extract powder with distilled water. This comes out to 1 around tablespoon malt extract per cup of water. Bring water to boil, and then slowly mix in the powder under stirring until the powder dissolves. Pour this medium into any large jar with a metal lid, and make one small hole in the lid with a nail. Cover the top tightly with aluminum foil, and either boil the jar in water for an hour (be sure to put the jar on a washcloth and not directly on the bottom of the pot) or use a pressure cooker set at 15psi for 20 minutes. Let the jar cool overnight.
The next day take your spore syringe, stick the needle through the hole in the lid, and squeeze in the solution. Cover the top of the jar with aluminum foil again, only not too tightly since you'll want to allow gas exchange. Keep the jar somewhere warm and dark, and agitate it every day. You should notice the solution becoming milky, and toward the end of the incubation you'll see fluffy pieces of mycelium floating around in it. At this point you can keep it in the fridge until you're ready to use it. When you want to start a mushroom culture somewhere, flame-sterilize the needle of a 10cc syringe, let it cool, stick it through the hole in the top of the lid, and pull in as much solution as you need. You can then inject this into your substrate and it will start growing immediately. Any time you run low on mycelium solution, go through the same process with another jar only instead of injecting spores inject the last of your mycelium solution. Be on the lookout for any contamination!