I can all but guarantee there's still boxes of trigger groups, receiver covers, sears and anything else you can think of in some long forgotten corner of a store depot somewhere even today.
And some of the last sks's to go through the refurb process for storage probably were in the 60s or early 70s.
I am quite sure that both then and today there is a formula for parts to guns produced they followed.
Such as for every 1000 guns we need 200 spare bolts, 300 sears, 50 assembled trigger groups etc etc.
I have never found what part of the soviet warehousing system looked after boxes of parts and accessories but i will find it one day and post it here.