Can anyone point Archangel (and me, to be honest with you) to a website or book that covers the process of covering a wooden sheath in leather?

Archangel,
Try doing a Google search for "sterling silver sheet". I found this on eBay with the same search:

http://cgi.ebay.com/STERLING-SILVER-...QQcmdZViewItem

It is pricey, just so you know. It probably will be, no matter where you get it from.

One place to try, especially if you have a business license (of any kind) is to find out when the next local gem and mineral show comes to your area. If you can get into the dealer (wholesale) side (for which you'll need the business license), as opposed to the consumer (seller) side, you can probably talk to some of the silver jewelry makers about where they get their sheet silver from. If you can't get into the dealer side, you can probably get the same info from one or two of the dealers on the consumer side (but you'd have more luck with the former).

Another source might be to find a local jeweler who works with silver and see if you can get their source or if you can buy from them.