Importing parts is completely legal, as long as it is not a complete receiver. Really, you've got to find a person you can trust, have whatever parts you like sent from the retailer to him/her. Then have him/her send the parts to you, as almost every retailer will refuse to ship to you.
If you go into the rules and regulations, parts solely for the function of a MG are illegal to import. However, this is limited to the Receiver only, and everything else is not technically limited solely to the use of a MG. Any parts kit with a demilled receiver is 100% legal for you to import and own, do not let anyone else tell you otherwise. I have gone though a lengthy process of contacting the Canadian firearms center, contacting customs, and other "officials" to come to this conclusion, it all boils down to if you are talking to a guy who knows his laws inside and out.
I imported my M53 parts kit in july, had it sent through Fed Ex. It spent approximately 2 hours in customs, and was then shipped directly to my house. Basically, no problems what so ever. I am having another member here help me with shipping my IMA receiver pieces to me. There should be no problem shipping it legally, unless regulations have changed in the last few months.
Marstar imports and exports via Plane, and therefore can ship their guns / parts without hassle. I hate defending marstar, but this is most likely their problem with SA mg42's: It is not them that is causing the wait, but their potential supplier. This supplier requires an exporting license, so that they may "apply" to receive export permits on an individual basis. This license, to apply to have permits has both an expensive fee annually, and a certain time period one must wait for approval. After being approved for the license, they must be approved on an individual basis for getting permits to export! It can be a lengthy process per say. Marstar can legally Import them as they please, whenever they like, but their supplier would have to be having legal issues with Exporting them outside the USA (thus causing the delay).
By the way, gun building is also 100% legal for non-licensed "normal guys", while keeping it within the boundary of non-restricted i believe though. Just notify the Canadian firearms registry of your serial #, and wait for the approval that such serial # is not already taken. Have an rcmp officer verify its "non restricted" status, and you are now the owner of your very own homebuilt gun

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Cheers to you too, and good luck with your mg34 purchase!