10/22 stocks are everywhere due to so many people customizing their guns. I've seen them sell for anywhere from $15 to $50. I would expect to buy one for somewhere around $25 or $30.
I just realized that you said "Sporter" stock. My sporter has a walnut stock. If it's walnut, I would think it would be more like $50 - $75.
Typical birch carbine stocks - a MINT one, brand new off a brand new gun might fetch $25 - $30 if it's got really nice grain. There's just WAY too many.
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As for the stock, on Rimfirecentral.com there's a Superstock forum that has a pay-it-forward thread. You could post it up on there and it would go to someone who would make good use of it. Be forwarned everything is given away with no expectation of payment.
As for gunshows.... over here in Arizona I attend gunshows large and small and have never seen anything happening that looked the least bit suspect. Maybe they do illegal business in the restrooms or something. :?