This was a response from Canon in early 2006:
EDIT: This is for a slightly different item, but I bet the response from Canon will be the same.
Thank you for writing to us. We value you as a Canon customer and
appreciate the opportunity to assist you.
The magazine is not sold alone on our website. You may want to try our
parts department.
For the price and availability of parts, please contact the Jamesburg
Factory Service Center below and select the appropriate prompts for
ordering parts.
Canon Factory Service
100 Jamesburg Road
Jamesburg, NJ 08831
Tel.# (732)521-7230
Business hours: 9 AM to 8 PM (ET) Monday to Friday
We hope this information is helpful to you. Please feel free to contact
us again if you have any other questions or concerns.
Thank you for choosing Canon.
Sincerely,
Phillip
Technical Support Representative II
Found here: https://photography-on-the.net/forum/showthread.php?t=139657