i personally have not tried, but i believe that importation is the opposite for mp5's in regards to the uppers being restricted and the lowers ok. it all has to do with the location of the real steel counterparts serial number location. that being said nothing is ironclad in regards to airsoft/firearm parts and importation.
EDIT: here is something pertaining to importation and MP5 parts
http://www.airsoftcanada.com/showthr...ight=mp5+lower