not sure whether you mean you want to find a bike like that or actually want to go through the mechanics of purchasing the bike.
If the second, you have 3 choices.
The first is to import the bike into Argentina legally and then transfer title under the Argentine system. I would guess that there would be considerable taxes to pay and it would be a real hassle. If you live there and speak spanish well then this is probably for you.
The second is to transfer ownership in the united states - which is relatively easy, but you almost certainly have to be there, and you need not just the old title but also a US drivers license (which comes free in packets of Cheerios or you can just take the test - you will need proof of address though...).
Make sure you don´t need a "safety check" when you transfer ownership - as the bike won´t be there to be checked.... Get the minimum insurance that you can as it will be useless to you in Argentina and SA.
Once you have the new title then you fly to Argentina, go together with the old owner to the nearest border, export the bike under the old title and owner bring it back into argentina or on to the next country using the new title and owner. done. If you live in or near the states then this is for you.
Thirdly you could just forge a new title and do the import/export thing. Just beware if you want to go back to the states... There are usually forgers in any big city - get a good job done... This is the simplest yet scariest option. If you have no money nor scruples then this is for you...