I don't want the one with the thumbhole.

The very 1st batch to hit US had stained black wood stocks.  But since Molot does not usually have this option, usually slant back thumbhole stocks, these black stocks were sourced elsewhere to complete this initial order.  These stocks also were shipped with out butt plates.  A couple vendors that did the initial preorders for the very first Vepr 12s actually thought enough to replace their supply with fitted poly stocks.

I bought my first one from Atlantic Firearms (preordered) in 2012 & they swapped the stocks out before shipping them out to customers.

So can I just get one aftermarket and do a swap?

I worked at TGI when the first Vepr12's came in. We were the first importer of the Vepr12. The ATF took forever getting our approval letter back to us. The shotguns had the original folding stocks, but they had a small spot weld to keep the stock in the open position.
We had some come in with the black stock also.