Excuse my ignorance, but is there something special about the banks cage, or just that it's off the shelf and will fit?
There are plenty of people who can make a cage to fit. I have a roll hoop with the project I've just bought, but not sure what kind it is. I'll check and see.
If you want a cage made to your requirements, try Tylah Motorsport (see on Facebook) or drop me a message for his number. He's in Bracknell, so not too far from you.