Your best bet is probably to find some coin shop around where you live to sell you silver. That way you can avoid shipping and perhaps an added service charge/premium.
That said, I sell silver art bars here:
http://www.bonanza.com/booths/SolidSilverThese are priced above spot because they're collectible. Also I prefer to ship FedEx which is more expensive than USPS. I would never send anything untracked. Even tracked with USPS is more of a gamble than FedEx, but FedEx is pricey. As a seller, the peace of mind that it will get there is worth the added cost. If it gets lost in the mail, I'd feel it was up to me to make it up to the buyer.
I never send silver without payment up front- I have 100% good feedback on Bonanza. I never sell more than three ounces at a time, and I wouldn't sell more than one ounce at a time for bitcoin.
I have a friend who has lots of 999 silver one-ouncers for sale right now... he sells to me at a buck or two over spot and then I'd have to tag on another buck or two to pass it on to you. Again, your best bet is to just find a local coin shop around where you live.
Right now the trend for silver is up, so there's not much incentive for holders of silver to sell. You're going to have to make it worthwhile for someone to sell.