scyther wrote:Are there any bullion bars or coins that are .900, or .925, or something like that?
Yes. Franklin Mint made all kinds of "collectable" sterling bars/ingots/medals/rounds. There are some other odds and ends from other makers too. It frequently sells at a discount to the melt value.
scyther wrote:If I melted 90% silver without purifying it, would there be any market for it?
In short, no. It would sell for even less than 90% coins because it would no longer be in a recognizable/verifiable form. I have tried to retail sterling bullion bars...they don't sell.