If anyone does have such files, they certainly couldn't share them with you
that would almost certainly* be a violation of copyright.
On the other hand, the Patricia Clark Memorial Library has a wide variety of free, public domain LRFs uploaded by our members:
https://www.mobileread.com/forums/ebooks.php?forumid=126
Perhaps some of them may give you inspiration.
* -- what is the likelihood that a commercial LRF was a Public Domain book?