There are actually a few options a person could look at if they wished to source a GBBR.
Initially they could purchase a GBBR in Canada with its clear lower receiver and once they have been age verified and gain access to a custom parts importer and they can source the required metal receiver you require.
GBBRs do pop in the classifieds and retailer listings as well so you can source your item that way.
If the specific model is not available then you could contact a special order retailer to bring in the model you wish.
You could always order from any other online retailer outside the country, you will pay less money however you do run the risk of have your imported item seized . Item seizure is disputable however you will require significant knowledge on the topic in order to launch a solid argument.
"Its only a little bit on fire"