When the FNs were retired from active Canadian service, something like 50,000 rifles were overhauled by Colt Canadaand put into war reserve. From which they went straight to the chopper.
I understand there are a *very* small handful of legitimate Canadian-made C1/C1A1s in the States, but the emphasis is on "very". And since they would have "walked" across the border and were probably never registered as machine guns (stupid auto-sear!), it's a safe bet they stay well out of sight.
Most of the C1s and C2s in the States are the result of literal years of searching for Canadian parts to build on a legal US made receiver. Very few parts kits made it over here, all parts are expensive, and some items, such as Longbranch-made barrels and many C2 parts, are made of unobtainium at this point.
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I've been told that rifles remaining in stock at Longbranch Arsenal/CAL were sold off along with the plant machinery and other assets when the Arsenal was closed in 1976.