[jabart]

Newer units (not all) in the US come pre-charged up to a certain size of lineset. Manufacturers can sell you a whole unit with a charge. The rest is easy to source locally though I haven't tried to get nitrogen myself.

Of course you have exactly one chance with your install this way until you have to call someone.

[mothballed]

nitrogen is available at any welding supply store. The container and pressure regulator is like $200 though.