I would be afraid, very very afraid.
400, 600, 800 are all available in single and 3 phase from every major
manufacture. Also available in indoor and outdoor ratings. Do you have a HD
CONTRACTORS store near by? The one near me has CH services sitting on the
floor, ~3K for a 600 amp.
Before you buy anything you had better check with your utility serving the
property. They will have requirements that must be met.
Phoenix has a company called Sun Valley Electric that builds fusible 400,
600, and 800 services. Usually you can pick one up the next day. The main
panel has 2 200 amp fuse holders. These are widely accepted here.