Help with sks not cycling

[edteach]

I took the SKS I bought from a friend that was bubbed up to the range. It would not cycle and I went home disassembled it and there was no tappet or return spring. So I need to source one. Anyone know where I can pick up parts? Thanks.

[running-man]

eBay is where I always look first.  Here's a Chinese op rod with spring as a package (though the op rod head looks like horsetrash, you might want to look for a better one):
https://www.ebay.com/itm/385868791438

There are Russian ones there as well that should theoretically work:
https://www.ebay.com/itm/133545069546
https://www.ebay.com/itm/275197827100

Numrich has the spring but not the rod.  Apex has both but it'll set you back $75+ after tax & shipping. 
Sarco, it seems has both at a good price (though you may need to call them as their inventory on the website sometimes shows in stock despite them being out)
https://www.sarcoinc.com/sks-piston-return-spring-new/
https://www.sarcoinc.com/sks-piston-extension/

Board members here may have them as well.  Greatguns sold a whole bunch of hardware a while back but I don't remember if these two parts were included in his listings.