Seller Silence

There is absolutely no obligation for a seller to answer your questions,  though it certainly would be courteous and beneficial to both parties. 

I see courtesy as a kind of obligation, one that especially benefits the seller. That said, the buy has the option to walk away or, if the purchase happens eventually, leave a rating of the seller that downgrades them for the communication component of the transaction.

Cleeds has it right.  If the buyer wants this info, the seller cannot provide it, only the manufacturer or importer can. 

There can be a number of reasons the seller didn’t respond.  Send them a second request and if they don’t answer, move on.  Give the seller a few days to respond, not weeks.