What denotes a quality SKS? What should I expect to pay for such a thing?
Where can I find the best of them?
What should I be looking for in terms of at least useful accuracy?
Can you recommend a source for goodies of the aftermarket persuasion?
How about ammo? How can I be sure of getting non-corrosive fodder?
A good refurb SKS will cost you roughly around $200-250. You may find one for less, but that's what I'd expect to pay. There are a fair number of dealers around...you might even get lucky at your local Canadian Tire. Don't turn your nose up at the idea of a refurb...I've got two of them that cost about $200 last year, and they look new. I see Tradex has a VG condition for $250...I'd be tempted to shop around at that price. Ellwood Epps has them for $189.
If an SKS looks good inside and out...no rust, maybe covered in oil or cosmoline, the stock in good shape, the metal finish not scratched or worn, that's probably the one you want. I don't think there's any particular make that's better than the rest. You won't get great accuracy...these rifles were meant to be fired at man-sized targets a few hundred meters away, so they aren't tack drivers. 3 or 4 MOA is about what I'd expect..you might get lucky and find better.
There's not a lot of aftermarket stuff for the SKS...I regard practically none of it worth having. I recommend enjoying this rifle in its original dress. However try the places that sell a lot of SKS's...they will probably have aftermarket stocks and other odds and ends, if that's what floats your boat.
Getting certified non-corrosive 7.62x39 isn't easy, and it's expensive when you do find it [and there are dealers who 'mistakenly' sold non-corrosive that wasn't]. I recommend shooting the surplus ammo and getting used to the idea of cleaning your rifle thoroughly after firing. Strip it, wash the action and barrel and gas tube first with very hot water, wipe clean and oil as normal [I like to spray the parts and interior with WD-40 to make sure the water is all gone]. It's the best practice anyway.
Tula was an manufacturing arsenal...'Simonov' is the name of the gun's designer...so all SKS rifles are Simonovs. Tulas are generally quite decent, but overall condition is the main thing. I wouldn't spend more for a Tula over an equally nice gun from another manufacturer.
Anyhow, have fun with your SKS...every home should have one.