In your initial post, you refered to the magazine as a clip. That could be part of why you have been having difficulty finding a suitable retailer.
Using whatever search engine you wish try typing in
"Tokyo Marui g18 hicap magazine"
"Tokyo Marui AEP highcap"
Im sure you will be able to find more than a handful of retailers that should be able to supply you with what you need and you should have no issues importing an AEP magazine into Canada.
"Its only a little bit on fire"