Did the seller list it as a "pre-sale"? Per eBay's shipping policy, "You're required to specify in your listing clearly and accurately when the item will be shipped. You're also required to ship items within 30 days from the date of purchase (see our presale listings policy for more details)." So unless it's a pre-sale item and he specifically stated when it would be available and shipped, he is in violation of eBay's policy if he doesn't ship it within 30 days.

I think what he's doing is auctioning off stuff, and buying AFTER he gets paid, so he's building in the time it takes him to get the bullion and then turn around and ship it to you. I can't fathom any other reason to take 25 to 60 days to ship something....geesh. Big risk though when prices are climbing...