Im no help for a source near you.

I believe that a snake can be kept in any size cage desired as long as its done correctly. My bp has spent its entire life in a 40gal tank(36in x 19in x 18in) and has thrived. I prefer naturalistic keeping and she has always had plants(fake and live), driftwood, and hides. This offers the feeling of security needed to keep your snake happy when the cage would otherwise have large open areas.

As for ordering a cage you can pretty much order whatever you want. I keep bloods and a brb in pvc cages that are 4ft x 2ft x 15in. They are good for holding humidity and easy to clean. I don't think a ball would ever need something like that though. For bigger snakes you can even get two piece cages that bolt together to be 7 to 8ft long. The sky and your wallet is your only limits when it comes to cages. My blood is nearing 6ft and she actually makes her cage look small. She only has a litter box hat(was a hide at one point) on one side a bowl of water in the middle and crumpled newspaper to hide in on the other.

All that said I don't think you would need anything bigger than a 40gal footprint for a bp,