Many website design companies do this with clients, putting "Web Design By company name" and adding a link either to the exact anchor text, or their company name. We experimented with this and found that there is a diminishing return on links like this, because our clients websites have nothing to do with web design.
This would probably be the same case for privacy policies for websites. Because the clients websites won't have anything to do with legal documents, it may not be the best linking strategy.
I do think giving it away for free is a good strategy. Instead of demanding them to provide a link from their website however, I'd try to get them to promote it on social media. Make easy share buttons from the documents with text like "We just got a free privacy policy for our website from (link to your clients company)"
Hope this helps