Its actually hard to predict what will really go fast. The market is changing so fast. Personally, I'd like a good source on new non-bipod cut handguards, but that is a part that is commonly replaced with US stuff to comply with the 89/90 ban. Still though, based on the condition of the handguards of the most recently available kits, there may be some interest.
Original STANAG scope mount top covers would sell like hot-cakes. You would have no competition.
New or like new Imbel barrels would be great and most likely sell if priced right. By right, I mean 10% or so less than whatever DSA is selling. Oh wait... you're in Argentina aren't you? A lot of those barrels are already here and selling cheap. The closed ear version may be good to import.
Small parts would also be good. Its getting harder and harder to find bolt hold opens the are not beat to crap and loose. Prices are also rising on them. Send a pile of those, new in wrap and sell them for $15 and you'd do well.