He took off the top slide and chamber?
Chamber????
Don't know exactly what parts you really need, but it does sound like you are missing the bolt.
There are a few places on the web that you could get a bolt as well as the other parts but you would run into problems with head spacing if it is the bolt you do need, and a gunsmith would have to check that for you before you would attempt to fire it if you did replace that part.
Check out this site, as Tapco now sells a new bolt that allows you to use the 20 round Tapco mag and be able to install a high capacity magazine without having to have the bolt open first which was a PINTA.
http://www.milsurpstuff.com/products.asp?cat=40Check out this forum as someone there would have or know where to get what you need!
http://www.sksboards.com/smf/index.phpJust a side note, if you have to buy all the parts from the sight back minus the trigger group be glad you were given the rifle, as those parts alone will probably run you half as much as a complete rifle unless you can find an individual that has those extra parts and willing to part with them.
Otherwise take it to a gunshow, and see if you can find the parts or sell it to someone, or work out a trade of some sort.