Are you talking regular Retics or dwarf? I'm sure you could find something suitable for a dwarf variety, but if it's a regular Retic you're dealing with, I think you'd be best to design something yourself.
Eons ago I kept mine in a converted room, which in my opinion is the only way to have a big old Retic get the amount of space and exercise it needs to be happy, healthy and easy to manage at adult size. It's a sacrifice to dedicate an entire room to a snake, but if you got yourself a Retic, you better be ready to make sacrifices in order to keep it happy, lol.
I really can't help point you to any suppliers or anything, I'm afraid. I avoid the entire reptile 'industry' like the plague, but I'm sure some web searches would turn up results. As to whether or not there are any Canadian suppliers, well...let's hope so because if you have to go outside the country you may have to sacrifice your own proverbial right arm in order to cover the shipping costs to get the thing here, lol