Yes you are correct in that each item has it's own page. These pages are not being reached by onsite links or a search function within the site, but rather they are being reached by indexed links from Google, bookmarks, etc.
If I understand what you are stating right this would replace any custom 404 error page that I have already and the visitors would be redirected to a chosen page "more than likely the home page". What I'm unsure of is would this also not return a 200 status ok ?

When a visitor hits a page that is not longer there they would get redirected "301" to another page that does exist, like the home page which would return a status 200. This I have done but I did it on the server side, not with a script. Google did not like it because it returned a status 200 rather than a status 404. Is there a difference of using a script or doing it on the server side, or am I really misunderstanding what it is you are doing? My main issue isn't really visitors reaching these pages, but search engines reaching these pages. It seems although I submit a new sitemap, it takes time for Google to remove the old or drop links that are no longer existing. Also having links from other sites that happen to pick up on a feed, that the search engines follow to get to a page that no longer exist.

I do feel what you are telling me to do will work, and will work well. I'm unsure if Google would see it as a status 200. That is where I am confused.