The reason for the lack of SKS parts kits is simple: economics!
AK/AKM parts kits are widely available (as are other "assault rifles") because the original guns are banned from importation. The parts kits with removed/destroyed receiver are not. The parts are always worth SOME salvage value.
SKS rifles, on the other hand, have always been legal to import as a legal semi-auto rifle, and are worth more complete than disassembled into parts.
Surely there are lots of SKS parts available. Check the Shotgun News, The Gun List, or some such publication.
HTH
John