The search is over !! I have been looking for a spare ignition key for my G5. After trying several hardware stores, none of them could make one for my motorcycle, I found one store called All Points Security Safe and Lock that had hundreds of keys of all kind. But they had never heard of a motorcycle called Royal Enfield. So the first clerk said NO, they don't have a blank for it. Fortunately a lady coworker looked up the name in her book and found that it is a British bike but didn't have any other info. She looked at my original key and gave me a blank key to see if it goes into the locks smoothly. I tried and it was OK. She told the first clerk how to cut it carefully. It has worked for handle lock, battery cover lock, air filter lock, and for ignition too.
I forgot to check if it will open the gas tank and the tool box. I will check it tomorrow. The key is CURTIS B-56. Only its shoulder edge is longer than the RE original key but with a little wiggle it worked. On the other side of the key, it says for GM cars.