EECOL, WESCO, WESTBURNE, TEXCAN all prefer to sell full rolls. If you ask for a cut length they normally charge more. They do it for us .. but we are an industrial customer so perhaps that changes things? I'm not sure.
If you are desperate, you can buy a pre-made 50 foot cable and cut it up to the lengths you need. Westburne has a part number for that. I don't have the part number handy.
Phoenix has pre-made cables too. I can't remember if anybody stocks them in Canada. Brad Harrison is the vendor that I think EECOL and WESCO carry.
These are suppliers, not stores. You need to be a business to buy from these guys. I don't know of anyone that does Devicenet in a retail store in Canada.
If it is for testing in a lab or an office, cat5 or cat6 networkd cable works in the Rockwell devicenet connectors for a 50 footer. Make sure you put the terminating resistors on each end.