In extreme case, stock could be "free". Here is a story posted on an auction site, saying the seller (auction house's client) received a C96 from a widow some years ago, it's identified as a "Flatside" variation. What they paid the widow was not mentioned, probably trivial. After a month or two, surprisingly, the widow mailed them another package -- it's the original matching stock of the pistol. "I guess it might be useful to you".
This flatside, along with the matching stock, was re-sold 2-3, or 4 years ago, I cannot remember. Of course, not that widow's asking price anymore. The service is not free. So, our mission is simple, bypass middle man and find such a widow, then everything is all set
So far, I noticed waiting such a widow to appear is much harder than finding rare guns, probably due to internet is popular these days, most widows are not in dark anymore.