First, I would contact the various companies you want to work with. See who is in your area already and see if it is feasible. For instance, I know SubZero removed several companies in our area and are only allowing one to be factory certified.
Second, I would find out who sells the appliances you want to work with and contact them about installing for them. If they sell them, they need a good installer. You might have to get certified or something with the factory first, though.
Third, best way to get into this might be to become a dealer of the appliances. Then, you could sell them, and install them and make both ends of the profit. Might take more cash and upfront money to get into this, however.