You can tell certain HK retailer are blacklisted already
RSOV is a really good example
Redwolf Airsoft is another one
Ehobbyasia to some extent.
I've never imported illegal parts but I did import alot of stuff that misinformed CBSA would think it's illegal (Airsoft suppressor, GBB parts like Complete Lower Receiver parts kit and bolt carriers) I got my stuff open quite frequently, to the point even hose, tank regulator are even opened. The only times it didnt letter mails.